Dan, first of all the inserts will work in the newer model backs so no change there if you were to upgrade. The lens work on all newer models except the AF (auto focus) so again no loss, unless you want AF. I have the even older 645, and find it to be a most reliable camera. You can get a metered prism for the 1000s, just takes a little hunting to find one - sorry I don't remember the model. You might look on the mamyia web site for more information on the camera and I think there are couple of books that detail the system. Hope this helps..if it were me, think I would stick with what you have if it in good shape and add a lens or two - I use the 55, 80 and 210 - makes a nice kit.

Good luck