I think the mining idea misses the point. This NASA plan is all about gaining experience surviving outside of low earth orbit.
1: Surviving without the massive radiation shield that earth's magnetosphere provides.
2: Surviving without an option for quick Earth return.
3: Surviving without near instantaneous communication with ground control, Major Tom.
4: Surviving extended exposure to zero-g (muscle and bone loss)
Well #4 has already been worked out a lot at ISS though the amount of exercise needed is significant (less mission time) and not perfect (still need to get strong again when back on earth).
Shall we start debating the need for artificial G via rotation?
Also #2 has been somewhat worked over with ISS, specifically the need for lot's of spare parts, redundant systems, and design for easy repair. What's not so well covered is, wetware repair. MedBay anyone? Is there a doctor in the house?