I have invested in early American bottles and pre 1872 American militaria for years. I also have investments in the stock market.
While I don't have millions of dollars stashed away in any of them, it is an amount that is significant to me and my lifestyle.
Given the choice now, I put my investment money into glass, militaria and decent antiques. The return on my $$$ in those fields have far surpassed than my returns from the stock market. The key is to learn your field, shop around, buy smart, purchase the best quality you can and stick with moderately priced items for investment (they draw a greater pool of potential buyers and are much easier to liquidate quickly).
One personal benefit of investing in these tangible items is that I actually have something to look at and enjoy. Of course there are drawbacks to owning them but every investment has pros and cons.
Wife and have have lived in a half dozen states because of transfers, new jobs, etc. We've made nice money on the homes we bought and sold, especially the two homes in Minnesota. Now that we're close to retirement, we're thinking about picking up some rental houses and seeing if they will appreciate like our homes did.