I think it is strange to have the diplomat from another culture be a vampire, visiting in vampire mode. If I were my mayor, I'd run screaming into the deepest reaches of my fortress and wall it over, before I'd hold a meeting with a blatant vampire. Instead, my mayor invited this Human vampire into her dining room and exchanged pleasantries while her children frolicked around him. I kept waiting for him to slay the whole family.
I didn't realize that we could turn vampires off. I thought they were like Forgotten Beasts, which I find much more difficult to deal with. Forgotten Beasts make fortress reclaim hopeless. Forgotten Beasts, in the guise of "Hill Titan", now appear aboveground for the "delight" of those of us who avoid meeting them underground. Personally, I had no idea that Titans could have the appearance of shelled slugs spitting poison, but I understand that if I want rid of them then I can go code my own game.
At any rate, I am not certain that I want vampires turned off. They do add flavor to the world history. I just wish there was some way of dealing with them other than locking them into a room for the duration of the fort, or sending them out unarmed against a Vile Force of Darkness. I also think it would be more cool for them to drain the Dwarves so they are pale, and possibly weak, but not dead. Vampires shouldn't want to kill off the herd. Maybe even some fraction could be converted into vampires themselves, by the feeding upon. But not all. Vampires shouldn't want competition for their food supply.