The only items made in mega numbers that are worth
much tend to be something
popular and never taken out of the original packaging (unused mint state).
Anything that I get in that state won't remain in that state for long
:-). I find it very unpleasant not to use a classic computer (or other
electronic, mechanical, etc device).
I think I've mentioned before that I once bought a still-in-shrink-wrap
HP71B service manual. That manual is moderately rare anyway (only
normally issued to service centres). Of course the first thing I did with
it was rip off the wrapping and start reading it. I had (and have) no
interest in it as an investment, I want to learn how the 71B works and
how to repair it.
-tony