Think I already posted this but
I think this thing should have a sequel on the wii.
Why?
The remote and nunchuck are ideal, because in the game Mario has these two handle thingies he squeezes, which could be set to like, B or C with a light press or a hard press. That's a bit difficult because unlike the L and R in the older game you can't really press it lightly, so maybe it could be B or C for light spray, and B+C for hard spray. A can be the jump button obviously. Since you don't have to press B to run like in other games that shouldn't be a problem. I think, unlike the old game, though, there should be several nozzles that you can switch to using 1 and 2 in Delfino Plaza, or whatever the new city would be, but in missions, this would be disabled.
The plot could be something like, there was some part Mario didn't go to since it had no shine sprites, but in time it became a monstrous beast, and in time it spread throughout the Isles. This new game would include levels from the old game minus Corona Mountain, but with 8 new ones each with a different theme, ranging from a deep forest with tribal pinatas, to a large city. These new ones would have to be vacationing spots like the old ones, because Mario would be traveling back for vacation. Level selection would be similar to Mario Galaxy 2, you choose levels from in a plane and land in an airport there. The final boss from the last game was kinda pathetic, so this one would require SKILLLZLIKZ
If there's anything else I missed I could add to that.