Its not finding gold and bringing it back here that's necessarily the draw. Its finding enough titanium outside of the gravity well to build a space station the size of Texas...

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.

Not really, you can take a small loss by consistently selling the entire global demand at a lower cost, and as we're talking about gold from space it would be exceptionally easy to deliver anywhere in the world. The other thing is that the processing cost for 'new' gold today is ridiculously high, where as from an asteroid like Eros it's purely mining costs that you need to absorb in the price not the billions of dollars of equipment required to get microscopic amounts of gold out of rock.

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.