There is the possibility of growing crops in Martian soil. [1] Nevertheless many agree with your conclusion that stations in deep space offer decisive advantages in their low-energy access to asteroid resources. [2]
Regardless of which path we take, the immediate technological prerequisite is the same: an economical way to send Earth payloads to space, i.e. a fully and rapidly reusable heavy-lift launch vehicle. That's what SpaceX is developing.
[1] https://phys.org/news/2016-06-dutch-crops-grown-mars-soil.ht...
[2] https://en.wikipedia.org/wiki/O%27Neill_cylinder
