In this particular case note that the Wii hardware is, to a large degree, a straight repackaging of the GCN hardware with a bit more RAM and a higher clock speed. That the Wii is not an extreme graphical advance over its predecessor is to be expected. :)
I do agree with you in general, though. Which isn't to say that graphical advances aren't still perceptible (compare SNES-era sprites to any of the positively gorgeous sprites from Odin Sphere or Rayman Legends), but at some point you cross a threshold where graphics cease being cringe-worthy and start being merely dated. FFVII is a cringe-worthy example, whereas The Elder Scrolls: Oblivion remains breathtaking to behold (as long as you don't look anyone in the face, that is).
I do agree with you in general, though. Which isn't to say that graphical advances aren't still perceptible (compare SNES-era sprites to any of the positively gorgeous sprites from Odin Sphere or Rayman Legends), but at some point you cross a threshold where graphics cease being cringe-worthy and start being merely dated. FFVII is a cringe-worthy example, whereas The Elder Scrolls: Oblivion remains breathtaking to behold (as long as you don't look anyone in the face, that is).