Almost no muts or mods become mainstream in the UT games. They never did and never will. Only small groups and clans really use this type of stuff.
Unless Epic puts it into a future bonus pack, additional content just won't make it onto most of the servers. Which is why all of the "let's fix the UI ourselves" etc. is pointless and a waste of time.
And myself, I avoid servers running most custom maps and fifty muts simply because I don't want all of that garbage choking up my system, most community hackers unfortunately don't know what they are doing, and too much of the hacked-in content is messing up people's UT3 installs.
Well I agree muts might not become mainstream and theres very few I'll actually play online much, maybe RPG invasion is the only one I spent much time in.
I do enjoy a nice list of compatible mutators though even if its just for offline play, with Epic providing them there would be less incompatibilities and less of a chance for peoples UT3 installs to get messed up.
I try to keep my UT3 install as clean as I can and stick to content providers I trust to do a good job, if I install something and it stuffs something up I can usually reverse it (guess installers should be the go) and I usually wont download from that person again unless its stated somewhere that the problem I had was addressed.
It was the same for 2k4 though, I was having problems with compiling UC2004 TC and a fresh install fixed it. The cache was just getting choked up as you put it, so I certainly see where youre coming from. The biggest problem for me hasnt been maps or muts with UT3 but custom models, for some reason if I try to run unpublished it crashes.
I kinda agree with RFlagg though, maybe what UT needs is more of a community deal happenin. Like get Epic in there sponsoring mods much like valve did with CS and TF2, ofcoarse not every mod will be an instant success but with Epic's name backing it up it shows there is a level of quality there, support and updates into the future. It doesnt need to be TC's only, when we look at 2k4 we see how different companies worked on different gametypes so maybe theres something in that as well
Certainly bonus pack is the way to go, I dont think it would be unfair if Epic chose some content from the modders to put in with theirs regardless of the MSUC.