Steve makes an excellent point.
Not only does scanning ensure that libraries/museums have a record of what items are theirs in cases like these, scanning would allow some of this rare material to be made available on the web for baseball historians and enthusiasts.
The Library of Congress website has, for example,
Spalding Baseball Guides from 1889-1939, digitized and freely available to read.
Those gems of baseball history that reside in libraries and never get read should be scanned and uploaded to websites, however the resources to do so are often unavailable. That would be a great volunteer project, if it could be coordinated properly...