I think it's all about how you set up your OS in the end.
Of course more ram is gonna do a better job. But I found 8gb pretty powerful for my needs so far.
At one point I had it running 18 UO clients across 3 virtual machines with 1 gb each, and could still play newer demanding games at the same time, with no slowdowns whatsoever.
I always keep my OS clean and tidy though.
On the other hand, my sister's PC wouldn't get fast with 32gb+ ram installed I think. That's how much trash she has installed...
So in the end, I suppose it all depends.
PS: I recently installed a new system for a friend who works with audio software mainly. High end stuff only. The PC uses up his 16gb of ram in no time, with the programs he uses...