Remember, when they find a gold asteroid, gold price will plummet, while bitcoin price retains its value...
If past history is an indicator, he will put his fortune to good use. Probably more companies or projects that will, one way or another, help towards his man in space goal.
Now you know what else "The Boring" company expertise can be used for...
As for "rare" metals, of course we do, we are using them in things like cellphones and what not. It just happens there is a bit of a monopoly of them to certain countries. Getting more from space, will of course lower the price on them as well.
Ever seen those super strong magnets in hard drives? That's a "rare" metal.
Bezos is, not wrong. But his idea won't be realized in his lifetime. Of course humanity should also think of building space colonies, but that will occur
after the earlier stage SpaceX is paving. To build those colonies you need resources, a LOT of resources, preferably extracted and refined in space itself.
Yes, unless you didn't know Bezos is thinking in building an
O'neill cylinder. If you don't know them there is one at the end of the movie Interstellar; the Babylon 5 show is centered around one; and of course there are plenty of them in Gundam (or just look in Wikipedia).