'Monsters' have usually been a product of the era when they become particularly big, revealing some kind of comment about that time period. Back in the day, you had the outsiders threatening a community, like Dracula or Frankenstein, then the bestiality within man himself, such as with Jekyll and Hyde. Zombies, as especially highlighted by Romero, showed a concern for becoming mindless, consumerism-driven drones. This new rise of vampirism seems to show a more internal threat, one that largely looks and acts like normal people; with the recent shows like Tru Blood and the like, vampires are pretty much accepted parts of society. The fact that vampires seem to be seen as increasingly attractive figures could perhaps show a fear inside people of being normal -- that these beings are attractive because of their superpowers, their superhumanism.
Plus, have to agree, their mingling with romance has really upped their appeal. Their preening and general glossy appearance certainly makes them perhaps the most attractive and sexual of the undead figures.