The big thing that went wrong was they had the perfect storm in 2012. They presented the worst route known to man that year, but a combination of factors came about that prevented the race from being the humongous failure it probably should have been:
1) Contador's ban meant no Giro or Tour for him, meaning the Vuelta was his only viable target year-long
2) Valverde had an illness and injury-ridden Tour and didn't show GC-wise, meaning he saved energy to stagehunt (successfully) and focused on the Vuelta
3) Purito had a career year and Indian summer and the Tour route being so biased to time triallists meant he didn't race it.
So these meant you had the top 3 Spanish cyclists, two of whom specialise in short- and mid-length steep ascents.
Then:
4) Froome fading from his Tour form meant you had an additional wildcard, though he dropped away in the final week.
5) The broadcasting of only the final 60-90 minutes of stages meant that the total lack of action in the early running was not as clear from the TV, making each stage look exciting.
6) With Fuente Dé we got a stage for the ages, and one of the few truly legendary stages the Vuelta has in its back pocket, the best since Pajares 2005.
This meant that the 2012 Vuelta, despite its abysmal route planning, was a resounding success, so Unipublic thought it best to repeat the formula again and again: lots of short-to-mid-length and steep HTFs and MTFs (Cav isn't right when he calls it 11 MTFs, it's 11 uphill finishes. Even so, it's too much). They looked at the races in the late 2000s and saw small gaps being produced and didn't think "gaps are getting smaller on our straightforward mountain stages. Let's increase the gaps by making the mountain stages tougher and lengthening the TT mileage to mean riders have to attack earlier". Rather, they thought "gaps are getting smaller on our straightforward mountain stages. In order to get bigger gaps, we need more of them, because if we have gaps of 15 seconds on ten stages, that's 2'30, that's a good gap!"
Of course, part of the problem is simple: Spain's best cyclists at the moment are Valverde, Purito and Contador, and they're all the wrong side of 30. If you remember back at the turn of the millennium, the Vuelta was much more favourable to the powerhouse riders - the likes of Olano were all-round enough to contend for any GT, but how else would you explain the likes of Ángel Casero and The Aitorminator® winning? Not possible on current routes. Hell, Isidro Nozal was rumbling up the 5% mountains of the 2003 Vuelta all the way to the penultimate day when he lost the jersey in an MTT. The two TT specialists mentioned above won in 2001 and 2002 on final day TTs (which have sadly gone the way of the dodo). The Vuelta at the moment seems to be designed to favour puncheurs and wispy climbers who can force their way up 20% slopes best because that's the kind of riders at the forefront of Spanish cycling. Just like how in Cipollini and Ale-Jet's heydays a whole bunch of flat stages materialized in the Giro, or how when Lance returned to the Tour the TTT came back.
When Valverde and Purito retire, maybe the Vuelta will change again. With Contador still around maybe it becomes an all-rounders' race again with some finesse climbs as well as hell-slopes. If he isn't, then maybe it becomes a pure climber's race for Rubén Fernández or Marc Soler, or maybe it's all up-and-down-all-day for Mikel Landa and a bunch of stages in País Vasco emerge. Or Lobato becomes a beast in super-long slightly hilly flat stages, so they fill the race with 230km stages with a hill or two near the end to be worlds prep but have Lobato win all the time.