Hell, if we're outside the well anyway, we could build the flippin thing from concrete.
In short, mining space solves just about all of our resource problems, up there and down here, forever.
The value of gold will only drop to slightly below the base price of every other company in the world. Once Mr Ore Processor in South Africa can no longer pay for his billion dollar equipment to sift dirt, then the price becomes fixed. It's like coal in the UK, there's still millions of tonnes of reserve, but until the price gets high enough there's no point in hell of mining it.
So yes, you can't sell 3 trillion dollars of gold in a single day and expect to get what it's worth at market value. The prospect is that, you could probably undercut every gold producer in the world and still make a tasty 1.5 trillion (or more when companies start going out of business) in the long run. You could run it like the oil industry, just supply enough to try and keep the price in a nice range for the foreseeable future.
Edit: My point is that you'll make far more profit mining it as pure gold than the current processes on Earth. From a little research, global demand is already almost 50% higher than the supply. So supposing you sell the global demand of 3800 tonnes per year at half current market price, would still be 50 billion dollars a year, every year for 30 years.
If you're wondering just how much 3 trillion dollars is, well that's like the entire cost of the Iraq War there in one rock. Hell, you could buy Alaska and still have like 2.5 trillion to spare.
This is the ridiculousness of the arguments against advancing space exploration and technology, because there's more gold in one rock than in the entire world. That's not to mention, there's predicted to be asteroids containing mostly platinum and even more precious metals. For an asteroid of similar size to 433 Eros containing only 10% of its mass as a rare-precious metal like platinum, well that's when you get the capability to buy out the entire planet.
So I call 100% bullshit on people claiming there's no economic incentive in space exploration. There's more precious metals than anyone has ever dreamed of, there just needs to be a little spending to get it. Once companies like Virgin and all the other ones trying for space flight and then lunar orbits, it isn't going to be long before one of them figures out they can get to a rock like Eros and mine the hell out of it.