But, if one colony happens to have a lot of water wells, and another happens to have a lot of farms, and yet another has a an abundance of mines and foundries, then there will be a need for a some type of trade and transport system.
I agree with e-maxx, different types of rovers or different classes of rovers might be a good way to go.
One way to go would to be to make a basic tug or tractor type of rover and then introduce different trailers or modules you could hook up to the Basic tug rover or place on the back of a rover.
Yeah, I know, it sounds like, "Mars Road Trucker." But, the concept is sound.