Also, just as I like the idea that sunlight doesn't strictly KILL vampires but just "de-animates" them, I like the idea that holy symbols deal psychic damage to vampires instead of physical. I think it was Fred Clarke who suggested that religious symbols create massive cognitive dissonance in vamps

The Discworld idea that any sufficiently powerful vampire is a true immortal and crumbling to ash is an inconvenience they can bounce back from