Vampires are only "mighty monsters" if the DM or writer wants them to be. In most vampire fiction and film vampires are pathetic monsters, killed by the score by any competent foes. Only rare "master" vampires are a threat. Yes, Dracula was a threat against a bunch of low level foes; the Vamps in BG are going against legendary heroes.iirc, tgm said he wanted, in the distant future, do something about turning undead. imo its too powerfull. mighty monsters, as vamps are, can be turned away or charmed but not explode. and i also have to say that level draining is nasty (i hate it. thats why i hate vamps) and a monk immune to it is not a good idea.
95% of the work of difficulty increasing mods could be taken care of by just quadrupling the number of XP needed for each level. Those who want to play low level characters going against deadly monsters could do so, while those who prefer the fast advancement of the original game could have it. Just a thought.