I've always saw both BTVS and AtS as approaching a common point from different perspectives, that point being more or less self-acceptance. I've always felt it was possibly the strongest "message" in the verse because it covered both shows, but coming from different angles. And my fav, both deconstruct the tropes the characters/mythology were based on.

I don't know how it necessarily translates to Firefly or Dollhouse, but I do think it was at least some of the point of the Buffyverse.