At the same time, the era when the Vuelta used to tailor its parcours specifically to try to attract big names from abroad and let them get away with murder was a large part of why the race has always been the weakest of the GTs; since the mid 70s and especially the early 80s the race has worked really hard to overcome that - think of Dancelli blatantly holding on to cars in 1967 and throwing a tantrum over a one minute penalty, then the next day taking the race lead from Perurena in generous sprint bonuses, or Ferdinand Bracke's team threatening to pull out over a thirty second penalty after he took an illegal feed in 1971, with the commissar forced to pretend he wrote down the wrong dorsal number even though Bracke was in the leader's jersey so should have been pretty recognizable.
The Vuelta has come a long way from those days when its provincial nature and willingness to improve its field meant that the teams of foreign stars attracted to it would sometimes take liberties with the race organizers' generosity to accommodate them, so while they do have to withstand a bit more than the Tour or Giro, they can't allow the riders to dictate the game to them. They have to decide which is more farcical: a Grand Tour which finishes with a péloton the size of the one riding a .1 race, or a race organizer who holds little authority over the péloton and bows to its demands as it flagrantly breaks the rules knowing it can't be punished. The Vuelta, since the move to September, may fear the days of provincial fields, but it shouldn't; the September location means that as long as there are riders who don't get their peak right for either May or July they will get at least a decent GC field, if the Worlds course is appropriately tough they'll get a good mix of contenders, and while there may be a couple of surprise winners in the recent history, it's a) not any more ridiculous than Hesjedal at the Giro and Pereiro at the Tour, and b) not because the field was awful - when Cobo won the field included Scarponi, Antón, Nibali and Rodríguez who were all hotly tipped for the race, they just made a mess of their race preparation.