A few years ago, a computer was a major investment, and so this made the parts themselves worth a lot.
But as far as hanging onto them these days, the main circuit boards are slow, and the very early hard drives are not really worth the fuss of using, as these days, we can get more storage space in a simple memory stick.
But, I have found a great use for old hard drives from computers that are of 'middle age'. They have a good enough size to use to backup my digital photo's. I have copied a second copy of my better pic's onto an old hard drive, and given it to a relative, so that even if my house burns down, I still have the family pic's.
One drive I had though, had a burned out circuit board on it. And it had some older pic's on it already that I no longer had stored on the main PC that I am using right now.
So, Hubby did some research, and found this site:
http://www.onepcbsolution.com/
And after a couple of emails to make sure he had the right product, he bought a new circuit board online, and it came in the mail a few days later, complete with instructions. So, for about 40 bucks, he not only got my irreplaceable pic's back, but now we have a spare, although slightly unreliable, hard drive, that we can use for the secondary backup storage that I mentioned. I might never lose any pic's ever again.