"asteroid mineral yields are not likely to be better than on Earth." False. See: Planetary Resources. Rare earth metals are much more common on many asteroids

"asteroid mineral yields are not likely to be better than on Earth." False. See: Planetary Resources. Rare earth metals are much more common on many asteroids than on the surface of the earth. During the formation of the planet, they tended to sink to the center, where it's very hard to get to. A single asteroid Planetary Resources is targeting has more than all the rare earth metals ever mined in history.