I don't see Nintendo realistically doing much more than maybe improving the textures a little and possibly increasing the framerate a tad. Anything further than that and you're practically going to building the game back up from scratch, which just isn't cost or time effective.

I'm really interested in how these titles are going to sell. Will they beat their GC counterparts?

Mario Power tennis should have a shot at it if a Wii Mario Tennis isn't released before late 10 or 11. (1.22M)

I don't think any of the Metroid Prime's will beat themselves though, but MP1 Wii could beat MP2 GC in sales (1.29M)

And I think Pikmin 2 should be able to beat the GC one (1.06M)

I would buy the metroids if they changed that crappy water.

BTW MP1&2 could be released in a single disc.

I'm partly in Number 2.... but I think there should e a 5th category for Nintendo Gamers who just didn't buy the games the first time.

I am considering Pikmin/Pikmin2 as well as Metroid Prime 1 and 2 giving that I really liked Prime 3 which I bought recently.

I'm in category #2. I would have bought MP3 with my Wii, but everyone said after using the MP3 controls the MP controls would feel unplayable. I ended up buying MP 1 week before "Play on Wii" was announced. MP is a great game, but my biggest grip is the controls. I will definitely wait for MP2 to be released and might even buy MP again if I like the controls.

I believe Nintendo mentioned in interviews that all Play on Wii games will display in true 480p widescreen.

I don't really consider it a graphical improvement unless it will improve things no matter what TV you use. I'm still stuck with Composite and 3:4 screen size, so 480p widescreen isn't going to do much for me just yet.
Then again, I suppose it increases the value of purchasing a TV that can handle that, but I still think it's primarily going to be the controls that make the difference.