[Joe]

Yes, agree totally.
Along similar lines I think shutter counts which can often be found from DSLR cameras is a long overdue aid to buying s/h, and will become more so as the earlier DSLR's get older. Its' a shame its not quite so easy with something like a Pentax K1000 35mm film SLR, where serial numbers can produce a red herring if a later model has had lots of 'actuations'.
Spare parts availability is a major issue with some film SLR (oddly some of the later cameras like Eos3000 being worse than some earlier models like A1).....I'm guessing spare parts issues will become a major factor with DSLR's too. I shudder to think how many Sensors will fail in future years