Everything is susceptible to wear, but moving parts are the largest target for wear. After the mirror, and shutter, the control buttons and switches may be next. Things like battery doors, CF card sockets, anything that is subjected to repeated stress.
Every part is replaceable, the cost to fix a joystick or shutter button will not break the bank. I notice that fairly low shutter count cameras have sold in the $2600 range, so you are saving well more than twice a average repair trip. I did see a high usage camera for a low price last week when I happened to be looking, but can't recall where. I see a reasonable camera with 80K actuactions on FM for 2400, but I'd buy locally rather than online if I were in the market. I also see a new 1DX on FM for well more than a new one using the CPW street price, so a buyer should always check current prices. As always, ebay prices are higher than almost anywhere else.