(1) work on lowering launch costs? We've been trying that for a long time: It's pointless without an industrial driver to get us up there in the first place. If you've got a lot of commercial traffic, you'll get economies of scale (presuming you don't try to give NASA a monopoly on access).

(2) Power generation is my pick: next to information (communication satelites) power is the commercially valuable product with the lowest weight. As a bonus you get a potential global warming amelioration technology: put solar power satellites in L1, and you can both reduce coal burning and reduce solar insolation.

(If we'd started working on this three decades ago when space freaks like myself were pushing for it, the world would almost certainly not be in the mess that it's in right now.)