Also, gold wasn't used to build things, so it contributes very little to wealth (jewelery and decorations notwithstanding). Having a huge injection of iron or uranium or tritium or helium or lithium or other rare and sought-after elements today would be an entirely different story.
Of course, the whole idea of bringing an asteroid to earth to mine is pure sci-fi at this moment, so this is all moot.
The one thing those asteroids have going for it is that it's already in space - so if you were planning on building a space station, space ship or something of that nature, you might be better off mining in space to produce the materials for it (and save the launch costs, for the one time cost of launching space mining and manufacturing plants).
Somehow Europe lost sight of that and the US seems to be on the same path.
So of course the whole country benefited.
As for some spaniards profiting, of course, it was still feudal, aristocracy profited.
But certainly some monetary easing can generate quite some wealth.
It is very easy to point out how an economy with perfect information and perfect cooperation has zero demand for money, but reality works very differently.