They struggle to see how it could be cost-effective, even with platinum and gold worth nearly £35 per gram ($1,600 an ounce). An upcoming Nasa mission to return just 60g (two ounces) of material from an asteroid to Earth will cost about $1bn.
(http://www.bbc.co.uk/news/science-environment-17827347)
So a back of the envelope calculation: Assuming that it costs as much to haul gold from orbit to Earth, and the Space X Falcon can haul 6.4+ tons per flight, we could bring down $167,116,800 of gold per flight. Since each launch costs $80M+, we're down to $80M of profit. However, this assumes we're just plucking gold out of orbit, not hauling asteroids to orbit, harvesting and processing the gold, and dealing with all of the logistics of this operation - which are bound to be very expensive. It's ambitious to be sure, but we're very far away from platinum as the new aluminum.
Price of gold per ounce: http://goo.gl/htL7b Falcon launch costs: http://goo.gl/SWZlw