Well I haven't even bothered to play rc3.2b or whatever the current version is on extreme random. The current version's extreme is identical or almost identical as far as I can tell to the initial extreme that came out with version rc3.1 I think it was called, and since I beat that I'm kinda apathetic about doing it again.
I did beat extreme upgrade while having a troll competition with some guy, replay is posted in the topic where everyone posts their wins, but as to why nobody else has posted extreme upgrade, well, extreme random is the ultimate challenge, so like you said, people just prefer skipping straight to it.
You only need try upgrade and random yourself a few times to see the difference. For me, hard random is more difficult to beat than extreme upgrade. The challenge of playing random comes well before level 50 where you can start hoping for an early purple tower. It comes at level 9 or 10 when you don't get that early 2nd family member you so casually and unconsciously have learned to rely on in upgrade mode.