Shortly before I found APUG, I had added a medium format rangefinder to my small collection of cameras. I had been using an F100, which as you say, is a good workhorse. I found the Mamiya so much easier to use, just the F-stop and shutter speed to set... not hundreds of modes in the LCD window. It was freeing in a way, and was a real shot in the arm creatively speaking. I liked the rangefinder so much, that I found an old Leica... really love that! The F100 is used much less.
That said, it always rains, and I rarely give up camera gear. Plus, I think it's way easier to use with flash, if I ever need to, than the other two cameras. And if speed is of the essence... well 'nough said.
I'd hold onto it.