The online system is not going to be changed until the next gen, better get used to it. Don't fix what isn't broken, especially if the fix is a major redesign... if tons of people are happily playing MK:Wii with the current online system, it's not broken.
NSMB:Wii would probably not work too well online. Its close interaction between players doesn't really play well with lag (like a fighting game, but worse as you physically interact - jumping on each other, etc.).
Wii Fit Plus is a minor-add on, and Punch Out is not a major game either. Just wait until the next wave of games and you will probably be happy enough.
My Mario Kart Wii friend code: 2707-1866-0957