Never mind what it's all worth. How can we get it where we can use it?

We're talking billions of miles away, with astonishing temperature variations and nearly pure vacuum. Spare parts are months/years away.

Then, it takes tremendous energy to mine/smelt. And tremendous pressures. How do you grapple with an asteroid in weightless conditions, to apply a drill to the surface? What do you hold onto? How do you generate the torque to turn the drill? Not from some kW power source such as used in existing satellites and probes. We're talking MW/GW power sources needed.

Then, drilling produces dust/grit by the ton. Where will it go? Just blow it away? There's no atmosphere to vent dust. It'll all just cling, hover and generally be in the way. Building up continuously as you drill.

There are 1000 such problems to be solved before we ever see the first ounce of gold (or whatever) from an asteroid.