Are old shop repair manuals worth anything?

You may very well have a gold mine. A lot of those old manuals aren't available anymore, be it online, on disc or in hard copy. If you can find the market that is out there, somebody somewhere needs that information. I would suggest going through them and making a list of what you have and maybe offer them on amazon or craigslist or ebay. Classic car enthusiast may pay big money for an original shop manual for a 67 el camino electrical system. Ya never know.