That's funny, I was wondering the same thing about our October trip to MNSSHP. I am probably not going to dress up, neither is DH, but we just said the other day, "I wonder what people dress like?" I assumed mostly Disney but I do like Bali's idea about easily recognizable stuff like farmers, cowboy, etc.
Hmm, I think it might be fun to dress like a "land" in the MK.
Like dress like spacemen and hang out in Tomorrowland.
Or dress like a safari person and hang out in Adventureland... blend in with the atmosphere.