> Relearning a new UI doesn't have any obvious benefits. People would have told me about the benefits by now.

Gnome for me has the benefit of being usable without ever actually touching the mouse. I can keep my fingers on the keyboard without ever having to lift my hand and push around the mouse to switch applications, to start applications, find applications. The only time I need to use the mouse is if I'm using applications that have some kind of obligatory/mandatory mouse usage, e.g. Blender or Gimp or the like.

YMMV.