Great out-of-the-box thinking, uaxuctum!
I love the idea of a smaller playset that you buy multiples of depending on how big you want the finished playset to be! Whispering Woods really could go on and on!
I'm really keen on Skeletor's Throne Room! That seems to be the most customized scene around here, and it'd be much more satisfying to pay $50 - $80 for that diorama than the $60+ for that Marvel Select Mephisto's throne.
I'd be interested in seeing the design for a Filmation style Fright Zone. What would be it's playable areas? There's Hordak's Throne Room (jeez, everyone has a throne room...) and Horde Prime's whateverthatiswhatisthataclifforsomething. Maybe a swamp of some kind outside for Leech and a lab for Modulok.