The Vampire represents the animal in us. The unsuppressed Id. The vampire can kill, can devour, can live however they like. They have the ability to seduce and have sexual relations with whomever they choose, whenever they choose. They can live for eternity.
Reading vamp books and watching vamp movies allows us to fantasize. Or even on a subconscious level identify with our inner beast.
Unfortunately it seems that beast has been tamed by sparkles and baby vampires. These new human like vamps are not what Polidori had in mind with the first Vampire.
The obsession with these new twilight vamps is a little more superficial. Many of these authors are creating a protagonist with an empty shell. One that any reader can "become" can imagine themselves as. The reader then has an easy time living through the same generic plots that make them feel desired if only within the confines of the book. It is basically no different than an erotic novel, for no purpose more than escape.