Doesn't actual vampire mythology (read: Dracula, Buffy, not Twilight, etc.) dictate that a vampire is actually a demon emulating a person's personality, but the person is actually dead? Because based on that, this question is nothing more than asking us if we would let someone kill us if they offered, only our body would be used for terrible things once we're no longer even around to see it. So... no.
EDIT: Also, the immortality thing. Not for me. I can understand the appeal, but I think it wouldn't be worth it. Anyone who thinks it would really needs to play Lost Odyssey; that game demonstrates the downsides to eternal life more powerfully than I could express.