I figure no one would (or should?) have both Wii Fit AND Wii Fit Plus. Should I make the words "Resort" and "Motion" small like "Plus"?
Actually, a lot of people might. They would have gotten Wii Fit when it came out, then picked up Wii Fit Plus when it was released for $20. I did. 
As did I, but then I sold Wii Fit, considering the entire game is included in the Plus version.
Also, yeah Wii Wii is weird, but the game title is not just "Sports" or "Music" it's "Wii Sports" or "Wii Music", hence the two Wii's. One for the game title, one for the system name. Just like SNES, kinda. "Super Nintendo Entertainment System", then just "Mario World" would be weird.
I don't think I wanna get rid of "Wii" altogether, but maybe I'll do a version with the word "Wii" small on top of the second word, kinda like the retail Wii Sports Resort has "Wii Sports" on top and "Resort" on the bottom.
The other thing is that, at least for me, I'm not printing a cover for "Wii Music" since it's one of those shiny covers (in the US at least), so I made the other covers match to it.