Ever heard of market forces?
What do you think will happen to the price of Platinum (or iridium, or anything) if you start shipping it in in 5,000 tonne lots?
Only a few wealthy collectors will pay MORE for extra-terrestrial Platinum group metals, and THEY can be accommodated by Mining the K-T boundary layer for material. Most users will pay LESS for a bulk commodity.
Iridium spark plugs are fantastic. maybe everyone will have them, but only when the price comes DOWN.