Robot tech might be rapidly improving (and actually by "robots" you seem to mean rolling laboratories like Curiousity rather than truly general purpose robots), but AI is no where near close to capable of replacing a technician/scientist on the ground (or even in orbit). Doing things remotely is massively slow. E.g. commanding a robot to pick up a rock and having to wait 4-24 minutes to find out whether it succeeded. It's going to be a long time before humans are obsolete.

Colonisation is a completely different question/goal to sending humans to Mars.