No surprise that the graphics for this game sucks. Koei had little/no experience with the GameCube; even those who did are open to new abilities with Wii in relation to GC (the greater RAM has made some features a lot more feasable).
Koei aren't the best for graphics anyway, and I bet their main graphics artists and coders are tucked away doing Fatal Inertia.
Still, this might improve, but I won't expect wonders.
SMG proves that Wii can pull of some good stuff in the graphics department, and I'm sure that's not the last good eye candy we'll see on Wii. I think all will be fine.