I think zero gravity factories could have a lot of potential. There are many things that can only be made in zero gravity or are created much easier in such an environment. Pharmaceuticals, chemical compounds of all sorts and metallurgy are things just barely researched so far, we've probably only skimmed a fraction of what is possible in zero gravity fabrication.
That said, I don't think raw resources will be very profitable. Iron is very cheap, its like 200$ a metric ton right not. Gold is still just shiny metal, without a real industrial demand for it, its basically just a fiat for price speculators to rip off silly people over. The stuff that's abundant in asteroids is pretty well abundant here as well. The important stuff to get in space would be more exotic materials that are rare or non-existent on earth like, H3, which is more then 2000$/ liter.
Anyways, a space-elevator would be awesome, but its also something far beyond our means and by the time it's viable we might have found work-arounds for every other problem space exploration might be posed as a solution for. If we could produce indestructible nano-tubes on a massive scale to build such a thing, we'd probably be making damn near everything else with it as well and iron prices would just go even lower.