The problem is the transportation costs.

If there were gold bars neatly stacked up on the Moon's surface ready to be loaded up onto a spaceship, it would cost too much to fly there and bring them back to make it worth our while. You could pretty much say the same for any commodity, from perfect diamonds to highly enriched fissionables.

If we had to go to the moon, locate ore, mine it and refine it, and then haul it back, it quickly becomes even more unrealistic.

Right now the only thing worth the cost is not a commodity, it is knowledge. This is why comsats and earth resources satellites and GPS systems are profitable, they tell us things we are willing to pay to know. But the zero-g ball bearing and flawless crystals businesses never really took off.

The tourist business has potential. Rich people are willing to pay a lot for their kicks. But the real payoff will be what they will be willing to pay if something goes wrong, they are stranded up there, and they need to get rescued. Now we're talking a real return on investment!

I'm not being facetious. It would work like insurance.
You pay before you go the full cost of your rescue mission, say a million bucks. If you need to get rescued, you're out a megabuck. If you make it back OK and don't need to get rescued, you're refunded 900 grand. The balance goes to the underwriter for profit and overhead. And nobody could fly without participating in the program.

It would be kind of like the Obamacare individual mandate.