Why do I have to waste all that disk storing copies of files that exist in \winnt\system32 in the hidden subdir \winnt\system32\dllcache? Including such important files as winmine.exe 220mb of wasted space! D'oh.

Same here. I was running low on space on my system drive a while back, didn't have the time to run out and get a new drive. The quick fix was sfc /cachesize=50, where 50 = 50MB. I can't remember if I had to manually clean up the dllcache directory or not ;)

Look here for documentation, and enjoy all that new disk space - for a few days at least.