Here's a question: I'm playing in an 8-player Might & Magic VI tournament, and I captured a Castle controlled by the Computer faction that had a Black Magic Amplifier built. Can I upgrade Vampires? The rules don't specifically prohibit it...
In this case, I think upgrading is allowed. I don't understand why Vampires are so disliked; Necromancy is much stronger, especially if you level up several Necromancers at the same time. Vampires are essentially only needed for battles against neutral creatures.