I'm not actually pondering vampires, though. For my own current idea-in-progress I'm thinking about faery lore. For example, how attached are people to the notion that iron repels fae? Is that a tradition readers like to see, or one they're tired of seeing? When it comes to faeries, what features are you tired of reading about, and what features must be included or else it isn't properly fae for you?
Something I've been pondering: when reading fantasy, how far do you like authors to veer from established traditions for a supernatural creature? If we're dealing with vampires, say, then they can't NOT drink blood. They aren't vampires unless they do. But can the author change other traditions and still make it work for you? It seems to have been voted a bad idea to decide they sparkle in sunlight instead of burning up, so apparently readers do have limits. :D