Sorry Chef, but I like n64forever's idea of putting whole courses from Mario 64 in a SSB setting. Why should Rainbow Ride/Cruise have all the fun.
One of my ideas before Melee was to have Wet-Dry World, with the ability to change the water level. The crystal taps would appear randomly (usually in pre-set spots), and when attacked, would change the water level accordingly. They could make into one of those..tour stages (like Delfino Plaza in Brawl) with stops near crystal taps, maybe even the downtown area..