I wasn't listing loss in values in various hobbies as an investment lament, but rather only as an indicator of the fall off in interest by the population as a whole. Both stamp collecting and model railroading have long histories of well over a century, showing continual increase in interest through several generations .... until now. Values were just used here because they are perhaps the best bellwether to show trends in activity and interest through time.
Yes, I agree, for investment purposes you can't beat dirt, as they aren't making any more of it, but it is difficult to take with you if circumstances force relocation. Precious metals and gems have historically always retained some value and are generally fairly portable. But ammo may well be the currency of the new millennium!
Perhaps I should add that I have no intention of selling any of my collections within my own lifetime, and really have no direct heirs so a niece and nephew will be the likely inheritors. I didn't buy anything in any of my numerous collections with any kind of profit motive in mind, but I did tend to gravitate toward things of at least some intrinsic value. These things were bought solely on the basis of expected personal enjoyment, and so far nearly all purchases met that standard, and continue to meet it, so it is most likely I'll die happily with it all still in my possession, and won't ever realize the profit or loss on any of it!