Dmian That's refreshingly nippy compared to the speed I'm rendering at for sure.
I definitely think some sort of cursor-based manual selection is in order. Random coords can be a nice surprise sometimes but the odds are very high that it will land in a plain area, which doesn't make for a very satisfying demo.
The images in the top post were rendered in SCREEN 10, although I was slightly cheeky and stretched them x2 in the vertical for upload. I left it rendering in SCREEN 4 today.
Here are some choice outputs from that session: