I just recently joined because of Elder Signs even though it hasn't launched here in Germany.
After playing some singleplayer sessions and 2 quick but successful 3 player games I have to say that I'd be really happy about expansion packs. I like Traverser's statement about new places. Maybe a new gameplay mechanic that allows investigators to travel to new places (new enterances) like the Miscatonic, Innsmouth or Dunvich.
I'm not sure how to combine it to the "fight" against the Old One's at/in the museum but FFG surprised us all over time. Maybe they'll find an attractive new way to do it.