Don't Complain if You Buy The Pack

My ideal game would have a settings screen you could bring up for each world that let you select some basic rules for NPCs in that world. So you could choose if vampires, aliens or spellcasters would appear in each world as NPCs. Your sims could go where they wanted when you are playing them, but when you're playing a different household they would only appear as background sims if you've allowed them in that world. That way you don't have to disable the vampire pack and never play your vampires again just because you don't want them in Sulani or Strangerville. And where you say they are allowed, they can use all of their powers as much as they want (well, maybe they could tune the AI a bit so the spellcasters don't cast inferniate incessantly and occasionally do useful things instead - but that's an overall autonomy problem).

If they could disable all outside NPCs from appearing on Batuu, they should be able to do something like that, I would think.