@sc94597
I think your estimate (in particular polygon performance) is way too optimistic ...
My main thought is that there is a practical limit to the polygon performance you would want out of a console that only displays at 480p. The number of pixels-per-second that are displayed at 480p is 20 Million at 60fps (and 10 Million at 30fps). After you account for wasted polygons by the limitations of our clipping, culling and level of detail algorithms, after you hit (roughly) 30 Million polygons per second you will be only adding polygons which are smaller than a pixel and thus add nothing to your image quality.
The area Nintendo (probaly) focused their attention on was improving texturing performance. The Gamecube's Flipper GPU had 4 pixel pipelines with one texture unit each which was able to produce 648 megapixels and 648 megatexels per second. It is not unreasonable to expect that (along with increasing the clock by 1.5 times) Nintendo doubled the number of pixel pipelines which would increase the number of megapixels produced to (roughly) 2 Gigapixels (explaining the comments that the Wii could produce graphics in 720p), and/or doubled the number of texture units per pixel pipeline which would mean that the Wii could produce 2 to 4 Gigatexels.
To take this discussion and put it into practical terms, the Wii can produce graphics at 480p where adding additional polygons or using higher resolution textures can not be seen. If you look at the better looking Wii games you will notice that there are few polygonalization artifacts, and the textures have almost no pixelization artifacts; everythin looks silky smooth.
