Research settlements are funky, funding agencies and scientists would be quite interested in understanding the geology dynamics on a tectonically dead world. Biologists will want to understand why mars never developed life. Medical researchers will want to understand the effects of isolation, and low-g. Donors, and funding agencies interested in these fields will want to fund expeditions. The expeditions will need infrastructure. The infrastructure's existence will motivate a few entrepreneurial expeditions.

Once the transit economics are understood, The Moon and Mars can both provide accessible surface deposits of water, iron, copper, and other commodities to orbit for less energy than earth. A number of activities for resource procurement for commercial space industries will be a tad easier when attached to a big low-g rock where an extra green house can simply be dug out. The relative lack of environmental externalities from mining and other activities may be a resource unto itself in the next few decades.

On a longer timeline - Mars could be given a tolerable atmospheric pressure and liquid water for <100 trillion dollars. Barring a change in global growth rates that would be ~3% of annual global GDP by 2120, and .1% by 2220.