I think the Mamiya 645 is a great camera. Two accessories that I find very useful are the gridded focussing screen (I think it is called the A4 Checker), and the power winder. The power winder, although noisy, allows me to operate the camera with one hand. Also, since I am using it I have never inadvertently tripped the shutter when changing my grip on the camera. Used to have a picture of my feet on every roll.
BTW nice spell checker!