I think it is "Newer" that has just come out with fast G3 upgrades for the Wallstreet. You could get one of these. Other cool stuff would be if you could find a DVD module for it at a mac auction site or something. You can replace the Hard drive for a bigger one cheaply too and more SD-RAM wouldn't go amiss.
In terms of the case. This part is the fun part. You can paint the center panel silver or something and it looks really effective. I think there was a forum a while back with some great pics. Basically tape up the sections you want to remain unpainted and protect all the important areas and spray the rest of the case the color you want. Check for that forum: the pics were awesome!