The biggest downside of the Mamiya 7 (II) is the body itself. Its innerts are made of diecast metal (dont'know exactly which one) and covered with plastic. The plastic is only fair made. I think daily use will very soon make the camera look like used for several years. The Mamiya 7 is definitely a professional tool and people who bought this camera know how to take care of it, so Mamiya didn't develop a body like the EOS-1 Series.
Sometimes I whish Mamiya would have made the Mamiya 7 like the Contax G-bodys: Diecast innerts and a metal surface. So the Mamiya 7 would be a camera with highest IQ and a durable body, since the lenses are made of metal.
Spending 3000$ instead of 2000$ and getting a durable body which would make the system even more a long-term investment and a long-term tool for me. The question for me is, what problems will appear in long-term use and what reparations will they cause? And could a more durable body prevent problems?
Besides this, I treat the camera like a raw egg.
I have an article from a magazine showing the diecast-chassis of the Mamiya 7 II, but I think showing it here could violate the copyright. It is similar to the Contax G2 chassis, but the rangefinder-module is set on top.