I don't have vampires in my books, but I do interview my characters these days. I haven't been consistent about it, and I sometimes go back and change the answers when I get a better idea, bit I'm starting to really like the outcome.
I recently reviewed an old interview with Steve Reyes (from my current WIP) and decided to change his fear to something interesting. That gave me a whole new idea for several scenes, and part of a plot twist. So, not only is he human and vulnerable–in spite of being a kickass DEA agent–I can use his weakness against him later.
Yes, our characters suffer for the enjoyment of our readers.
Unlike a job interview, I can ask my characters the most personal Qs. Biggest fear? Worst day of your life? Age? First time you had sex? All fair game. And even though I'm the one providing the answers, I'm often surprised by what they are.
Do you interview your characters? If so, what kinds of questions do you ask?