I had a conversation a few years ago with Buzz Aldrin. He was talking about his idea for a Mars Cycler which would travel continuously between Earth and Mars. I told him that I thought it was a great idea (especially as it would be investing in 'permanent' space infrastructure instead of a single-shot mission) but that I thought it was unlikely that the government would allocate enough resources to build it. He seeme…
Right now Mars doesn't have any resource with crave enough to justify this enormous cost. If suddenly we discover that there is something we can get money from, and not just knowledge, you'll get investers.
There are certainly places in the solar system that do have valuable resources and the fuel to trawl around the asteroid belt would be a lot cheaper if it could be lifted from Mars rather than Earth.
Not saying it will happen anytime soon, but that may be what the future holds.