I have wondered about this topic before. For that reason I am trying to limit the size of my collection. I have never been an investment collector, I never even saw myself as a collector anyway. I just like to play with the stuff! At least most things are worth something when we decide to let them go, as opposed to the RC helicopter items which are virtually junk. Servos radios chargers-all almost no value. The only upshot is a LOT of the tools are good for other small hobbies and modeling.
I think there will always be a small number of people that are fascinated by physics and mechanical movements. I came into steam engines a little late and just in the last several years I can see the hobby dwindling. It all ebbs and flows but demographics play a big part in current trends.