[dsfyu404ed]

I'm not sure what the net tonnage of robot missions we've sent to mars to date is but that level of knowledge we've acquired is on the same order as what we'd get from a couple humans spending a week there with a bunch of tools and scientific instruments. Humans ability to improvise lets us quickly identify what is of interest and study it saving us from having to send multiple iterations of robots.

For any given fixed distance (e.g. mars) at some point there's a crossover where sending some people up there to go kick rocks is actually cheaper than sending a series of robots that kick rocks in progressively more detail. I'm not sure if we've reached that technology point yet but as space flight gets cheaper and cheaper it will eventually happen for the moon and then for mars.