The estimates I've seen for a human mission to Mars are about 100-500 times the budget for Curiosity. So even if astronauts could accomplish things 52X faster (and I'm skeptical they would), it still wouldn't be as cost efficient. And that's even before you factor in the fact that the Mars Rover is going to be doing work on Mars much, much longer than a human mission would (Curiosity is going on 8 years).
Human space exploration is a solution in search of a problem. People don't seem to be rationally looking for the best way to get certain information from Mars or for the best sources of materials that could be obtained with future technology (there are many overlooked terrestrial ones) and soberly deciding that astronauts are the best answer. They seem to start out with the goal of defending human space exploration, and then searching for problems to try to justify it.