"they could easily reach planets with megatons of the stuff" (re: recycling v-ger for its gold)
right, heavy elements (like gold) are quite possibly more common on inner planets, and if you mine stuff at night, and at the poles, not unreasonably hot either. If I had the tech available, I'd certainly give it a shot.
the basic logic: outer planets are nearly all 'gas giants', inner ones are rocky. It seems to me that heavier elements collect closer to a star than farther away from it. Conclusion: Mercury probably has more gold than Earth.
asteroid mining would give you easier physical access to "everything", too, but how much gold, platinum, and other 'rare earths' being present in asteroids is still completely unknown.