I think this is a good title for this thread. Here's a piece written by Graham Womack about the work to conserve a vast baseball collection of a SABR member, a one-time minor league scorekeeper, among other things. It looks like it will now be housed at the San Diego library.
http://www.sportsonearth.com/article/66450530/
It's a fascinating piece and there's a few scanned images of a survey the owner had players fill out (likely on 100K players!).
I've often wondered about even just some smaller collections. My friend who played for the Reds minor leagues in the 50's has a scrap book his mother kept of his playing days. Another buddy and I sat around one evening having a beer looking it over. One article from his B League season reported him giving up a home run to Brooks Robinson. I plan on talking to Don about what his plans are for posterity.