Even the much cheaper S7500 gives a pretty decent result at 640x480, once you tweak the white balance, saturation and contrast (the auto settings aren't much good). I know this because I've been playing with one tonight.
RightLight works pretty well: I was able to use the webcam in a dark room with just the pilot light from the camera and the illumination from the monitor, although obviously results are better with proper lighting.
The 9000 adds auto-focus (manual wheel on the S7500), which sounds like a good idea to me.