It's not so much about a dilution of interest in World Tour races, but that for a period some races' value was artificially inflated by the Pro Tour and then the World Tour. Some odd choices in which races got to be World Tour often sparked debate when discussing those races, as much as the races themselves, and races like Vattenfall or Plouay never really raised huge amounts of discussion anyway, even if more than today. World Tour status was key for teams for a couple of years once the UCI tilted the balance further toward points to prevent teams getting all the benefits of ProConti and locking off wildcards by not going ProTour like Cervélo did, plus there was that time when the UCI was at loggerheads with ASO/RCS/Unipublic over who got invites, as the GT organisers had come to an arrangement to invite the ProTour teams based on who was originally in the ProTour, and then the UCI kept downgrading teams from their home countries in favour of moneyed Johnny-come-latelys and vanity projects, such as Sky, Radioshack, Leopard and Katyusha, meaning a lot of the local teams had to get a lot more out of their wildcards to survive and/or return to the top table. The resolution of that conflict has stabilised the top tier, and now the wildcard teams aren't all that wild, for the most part, and very few riders at the ProConti level are established stars - maybe only Bouhanni and Barguil would fulfil the criteria of both being established and being star names that are still at some level of power; people like Pozzato are established but are clearly past their best, while the other top ProConti riders are people like Ivan Sosa who are moving on from that level.
However, with the expanding of the World Tour concept that has come in the last year has also come a significant diminution in the World Tour status. One of the things that was best about the World Tour was that you knew all the best teams would come to town (even if they sometimes didn't want to, cue Euskaltel-at-Roubaix jokes), and one of the things that was best about not being World Tour was that the local teams could come and play against the big boys. This did inflate the importance of races with the status, and now that attendance at World Tour races is not compulsory for all of the WT teams, we are seeing those races return to their 'real' status level, so the field being drawn is no longer as strong, especially where calendar congestion is a factor.
The other problem at the World Tour level is that the concentration of budgetary power into the hands of a few does make the races a bit more samey, there may be 18 World Tour teams but there isn't the feeling that it's a level playing field between those in the slightest; the concentration of multiple star names in the hands of a few teams has led to a couple of teams being ridiculously over-powered - Quick Step in the Classics, Sky in the GTs - which leads to a lot of repetitive results. And the presence of an unpopular champion or two never helps, for reasons I've been through with my combat sports analogy before. There is also the over-representation of certain big-time races in the television calendar that if anything stifles the interest - a flat stage at Le Tour gets 4 hours of coverage, but if you've sat through that, you have no inclination to watch another hours' highlights of something else later, because you've a) already watched several hours of cycling, and b) probably got bored during it. And that's another factor - the lack of truly wild wildcards and the success of train templates in all formats of the sport, as well as the UCI's points system rewarding placements far more than stage wins or secondary categories, has meant that, aside from a small section of the northern Classics where that hasn't been able to smother racing to date thanks to the narrow roads and poor surfaces' inherent risks meaning all of the strongmen need to be at the front, not carefully protected until the last 10km, the type of riders most favoured other than those in the big bonanza budget teams that buy up the talent are those whose modus operandi is "fall backwards as slowly as possible"; there is no longer the same dare-to-dream value inherent in being a rider like a Thomas Voeckler or Johnny Hoogerland, and that kind of baroudeur is increasingly rare (shouts out to Thomas de Gendt and Tim Wellens for keeping the tradition alive), whereas the Tadej Valjavec and Haimar Zubeldia school of stage racing is seeing increasing numbers of applicants. Predictable and anodyne racing will always see people move away in much the same way as the F1 audience dwindled in many markets during a five year period where the only question was "how much will Schumacher win by" and "on what lap will Barrichello be asked to pull over"? Why watch four hours of a race if you know what's going to happen beforehand and don't like the result?
Another particular factor this year is that the World Championships are an especially hard parcours. The August and September calendar is greatly affected by the Worlds, because many riders rest up after Le Tour, so for a lot of the races their value for Worlds tune-up will affect both their startlists and the audience attention. Even the Vuelta sees the Worlds course affect its startlist, although it's usually stagehunters that are affected by this (nevertheless in 2009 there was a lot of 'Worlds preparation' going on from people who then contested the overall but wanted an easy out if they didn't have the form). With the difficulty of the Innsbruck parcours, the value of races like Plouay, Quebec and RideLondon to give a marker for World Championships form is next to nothing and the only races of requisite difficulty going on right now are the stages of the Vuelta, which further diminishes people's interest in those secondary one-day races.
Add to that the rise of other media for reporting and discussing races and the overall downturn in the use of forums, and there you have it.
However, with the expanding of the World Tour concept that has come in the last year has also come a significant diminution in the World Tour status. One of the things that was best about the World Tour was that you knew all the best teams would come to town (even if they sometimes didn't want to, cue Euskaltel-at-Roubaix jokes), and one of the things that was best about not being World Tour was that the local teams could come and play against the big boys. This did inflate the importance of races with the status, and now that attendance at World Tour races is not compulsory for all of the WT teams, we are seeing those races return to their 'real' status level, so the field being drawn is no longer as strong, especially where calendar congestion is a factor.
The other problem at the World Tour level is that the concentration of budgetary power into the hands of a few does make the races a bit more samey, there may be 18 World Tour teams but there isn't the feeling that it's a level playing field between those in the slightest; the concentration of multiple star names in the hands of a few teams has led to a couple of teams being ridiculously over-powered - Quick Step in the Classics, Sky in the GTs - which leads to a lot of repetitive results. And the presence of an unpopular champion or two never helps, for reasons I've been through with my combat sports analogy before. There is also the over-representation of certain big-time races in the television calendar that if anything stifles the interest - a flat stage at Le Tour gets 4 hours of coverage, but if you've sat through that, you have no inclination to watch another hours' highlights of something else later, because you've a) already watched several hours of cycling, and b) probably got bored during it. And that's another factor - the lack of truly wild wildcards and the success of train templates in all formats of the sport, as well as the UCI's points system rewarding placements far more than stage wins or secondary categories, has meant that, aside from a small section of the northern Classics where that hasn't been able to smother racing to date thanks to the narrow roads and poor surfaces' inherent risks meaning all of the strongmen need to be at the front, not carefully protected until the last 10km, the type of riders most favoured other than those in the big bonanza budget teams that buy up the talent are those whose modus operandi is "fall backwards as slowly as possible"; there is no longer the same dare-to-dream value inherent in being a rider like a Thomas Voeckler or Johnny Hoogerland, and that kind of baroudeur is increasingly rare (shouts out to Thomas de Gendt and Tim Wellens for keeping the tradition alive), whereas the Tadej Valjavec and Haimar Zubeldia school of stage racing is seeing increasing numbers of applicants. Predictable and anodyne racing will always see people move away in much the same way as the F1 audience dwindled in many markets during a five year period where the only question was "how much will Schumacher win by" and "on what lap will Barrichello be asked to pull over"? Why watch four hours of a race if you know what's going to happen beforehand and don't like the result?
Another particular factor this year is that the World Championships are an especially hard parcours. The August and September calendar is greatly affected by the Worlds, because many riders rest up after Le Tour, so for a lot of the races their value for Worlds tune-up will affect both their startlists and the audience attention. Even the Vuelta sees the Worlds course affect its startlist, although it's usually stagehunters that are affected by this (nevertheless in 2009 there was a lot of 'Worlds preparation' going on from people who then contested the overall but wanted an easy out if they didn't have the form). With the difficulty of the Innsbruck parcours, the value of races like Plouay, Quebec and RideLondon to give a marker for World Championships form is next to nothing and the only races of requisite difficulty going on right now are the stages of the Vuelta, which further diminishes people's interest in those secondary one-day races.
Add to that the rise of other media for reporting and discussing races and the overall downturn in the use of forums, and there you have it.