I was raised in a solidly upper-middle class family who had really strong values and excess was not one of the things that my family put up with. And there's something wildy decadent about the young-star lifestyle, and I just don't really see the point.
I always thought of vampires, especially the young-adult ones, as a metaphor for sex - sucking blood, forbidden, taboo. I think they just ooze sex. Vampires are all the big themes in life in one attractive, bloodsucking package.