My personal theory of how this will play out is that Mars will be a shallow gravity well industrial base for solar system development. We take for granted how integral gravity is to pretty much every thing we do when it comes to building stuff. It's not known if there will ever be large scale industrial activity in zero gravity. O'Neil cylinders are a solution, but expensive to start. If you can either mine Mars or process astroidal material there, it's a lot cheaper to get back into space from Mars than it is from the moon.