An all monster town-The town would have a grave yard, branchless trees,etc.One house would be a school called " Monster High ". You would want to use the manniquins and dress them in the Halloween costumes.Another house could be Frankenstein themed.Theres lots of items in the game that could be used for that.Another idea is i have seen lots of cafes,but never a creepy one.You could refurbish some pieces with the spiderweb shirt.Another house could be a haunted ghost house.It would also be cool to have a vampire or werewolf house or room.
What are some of your interests? What kind of town do you want to have? It's hard to suggest something without knowing what you like. In my opinion, if you're going to have a theme town, it's more fun if it's a theme related to something you really like, especially if it's your only or main town.