One "resource" that might justify a human presence on Mars is its relatively weak gravity well. Combine that with fuel production, and you are looking at Mars b

One "resource" that might justify a human presence on Mars is its relatively weak gravity well. Combine that with fuel production, and you are looking at Mars being the gas station to the solar system. 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.