I use a gauge like that for various tasks on my MB Diesels. Setting wheel bearings, correctly assessing timing chain wear, etc. all require a tool like this, and a good base.
No idea on value, but since you can get quality old Starrett and other high quality Euro and Japanese ones for $50-100 (or less), unless this one has some special meaning to railroad memorabilia fans or something, I wouldnt expect it to be worth that much more or less.