Well, gold isn't a very valuable thing, aside from it's use as a basis of currency and "look at this gold, isn't it pretty, I'm so rich!".

But there are other things that are more valuable. On thing is He-3, which would make an ideal fusion fuel. Another is pretty much any raw material, and the industrial base to use it. I'd much rather have industrial machinery churning out tons of pollution on the moon then on the earth.