Bringing down precious metals to Earth isn't the main point of developing space mining tech, e.g. mining a golden asteroid. The mined materials would be useful

Bringing down precious metals to Earth isn't the main point of developing space mining tech, e.g. mining a golden asteroid. The mined materials would be useful for bootstrapping other space based projects. With the right mining tech in place, it would be better to build anything that's going to be strictly used in space, well, in space. Earth's gravity well is much less of a cost factor if you don't have to send up manufactured items.