I agree that it gets spammy, but it also works. I've played warped 3 times through this. But I also think you can only do it so much... Like you said it gets pretty annoying, and super saturated.
Some of my friend's bands have also played it multiple times. I agree that it can help some, but I wish there were ways to regulate this, like only allowing people to vote for 2 weeks before the date, or something like that. Sadly, every little post made promotes the tour, so that will never happen.
My main issue with this is that the bands spam the hell out of everyone, and then it's not even that good of exposure. Most people don't stop and listen to smaller bands when there are tons of bands they've actually heard of playing at the same time. Yes, there are exceptions to this, but I have seen dozens of local bands play Warped Tour and only perform for their friends and family. Sure, you can say you've played Warped Tour, but it is very hard to gain fans and network just from playing one date on the smallest stage.