Even if Nintendo moves forward with hardware that is far more powerful than the current HD consoles (which I think is likely) I don't see Nintendo ever focusing as heavily on producing "HD visuals" as companies have been with the HD consoles ...
A lot of Nintendo's games (including most of the Mario spin-offs like Mario Golf, Mario Tennis, and Mario Party) are based on an artistic style which doesn't really benefit all that much from advanced shaders, and so many of the games share artistic assets that they should be able to reuse content from one game to the next.
Certainly, Nintendo's biggest franchises (Mario, Zelda and Metroid) will probably get a full upgrade to the latest and greatest visuals but (unlike current generation games) there will be a lot of experienced people to help them navigate the potential downfalls and a lot of mature toolchains to reduce (unnecessary) work.
