Right now i really don't know what to do with my Baronmayorbookkeepervampire. I danger-roomed him out of curiosity and holy moly is that a broken mechanic: legendary in shields in less than two days, legendary with weapon in less than a week, legendary armour user and dodger in a bit over a month i think. I managed to get 4/7 water in his tile and now he's a legendary swimmer, too. Problem is i can't let him out or he'll go on a citizen-guzzling rampage, because he's stuck in 'on break' mode - he's in constant feed mode and won't ever get out of it, only the fact that he's kept behind locked doors keeps my citizens safe.
He's also a lover of large gems. So far, my fortress has managed to produce two of those, in ~3 years, from ~200 rough gems. Of course, that meant one mandate failed and a fisherdwarf was picked out to go to jail. For 101 days. She survived, because i had her chained up in the middle of a food stockpile. But the next large gem mandate is only a matter of time.
The vampire would be an awesome fighter (must be something like legendary +200 or so with shields and axes), but i'd need to find a way to release him on enemies without giving him a chance to get near my citizens. I can't order him to do any work himself, because he's on break. So i'm more in favour of driving him mad; if he doesn't berserk, he can still serve as fort life insurance _and_ would release his bugged stranglehold on all diplomacy: his first meeting with the human diplomat never properly started, and now the humans send no diplomats at all, while the dwarven diplomats don't even try to meet him, they just hang around in the meeting hall instead of sneaking around the vampire's office; seems they still wait for the vampire-human meeting to play out, which with a dead human law-giver isn't going to finish anytime soon.
Oh, and who said vampires' attributes get locked? Mine went from 'very weak' and one positive physical attribute ('robust', i think) to "absolutely inexhaustible, basically unbreakable, amazingly agile and very strong". His mental attributes rose substantially, too.