I had a really nice looking Gateway desktop case I modded a long time ago. I painted it red (leaving some parts gray), added a fan to the top, one on the front (hidden) and removed and filled the old "Gateway 2000" logo. That was quite a while ago, though, and I've not done anything too major since...
I do have my NAS I recently removed the fan and replaced with a much larger, more quiet fan. Perhaps I could clean up the cut then paint the case
I recently noticed some scratches in the plastic, so painting it wouldn't be that bad of an idea