If we go grab a moon sized ball of gold, gold will lose most of its value. It'll be the next Aluminium.
There is precedent. When the Spanish extracted all that gold and silver from South America and shipped it back to Spain, all they got was inflation.
For platinum or iridium, making it cheaper there would enable all sorts of catalytic chemical processes that are prohibitively expensive now. If abundant enough, new demand will keep the bottom of the market from falling out.
Gold is excellent for contact points though as it does not tarnish.
Silver conducts heat and electricity the best of the three, but tarnishes the most easily, so it can have issues with high frequency signals as most of the signal travels on the outer surface.
If both silver and copper were the same price as copper, it'd probably be silver that would see the most increase in use in electrical applications. During the Manhattan project, there was a shortage of copper and cost was not an option. 430 million troy ounces of silver from the West Point Bullion Depository was melted down and used to make magnetic coils. At the end of the project, it was all returned, minus 120 oz.
If we doubled oil supply tomorrow, the price would drop drastically, probably to less than half. The total price of all the oil would be less than yesterday. But, that doesn’t mean we’re deriving less value from the oil. We’ll have more energy and materials, that’s more value. It probably isn’t twice the value (we’d probably be less energy efficient, for example) but it would definitely be more value.
2. They will likely be using mined material from asteroids to build space stations and bases.
3. They will only mine as much as they need, given an how much of it is available.
Its like expansion of human cities you extract/mine as much as you need and when you need it.
Space economics is a crazy thing, once you start thinking about it. The first people to start building in space will ponder the vastness and almost a infinite space full of resources and real estate to occupy. Of course the concept of ownership will look ridiculous. This is at least until there is a rapidly growing and spreading population in space.
Beyond that its really how quickly you can spread out. And the economics of that is not money. But trading energy for longevity.
I can assure you we are a very long time away from spreading to the last inch of the universe.
If I do it, I don't think it's in my best interest to announce it like that.