It'd be neat if Space Pirates wandered around in that little area in the distant background.
I would like the background to change to microgamesv occasionally, without the stage changing at all. Personally, I miss the microgames, at the very least, they deserve a visual reference.
You know that cave that the stage passes? It'd be cool if there was a Donkey Kong Country character sleeping there or something.
It'd be cool if those dwarf angel things flew around occasionally.
I miss the statue, cannon, and other aesthetics, though they'd probably be hard to do within the hardware limits.
Kirby enemies operating the cannon. BAM.
I would like a reference or two to the Melee Flatzone.
Yoshi's Island (SSBB) - I just don't like this stage. Maybe a 3D remodel or some background aesthetics would be nice. Oh well!
Onett - There's so much potential with background characters. I would love to see some hippies, dogs, or gangsters running around.
Brinstar - A change I want more than anything is a redesign to make it similar to Brinstar. Meaning Ridley flying in the background, the occasional enemy, that weird block platform on the right, and maybe the whole stage should be bigger and more vertical. Without removal of the acid, of course. Can they make the acid use the green fire element?