Quick note on the mars rovers--they weren't designed for speed, remember they were only supposed to last 3 months!
Next generation rovers will probably increase speed of travel significantly and the 2mph that men walk will quit looking so fast.

Robots keep improving giving more for the dollar. You still have to have all the remote sensing and robots even if you take men. Virtual telepresence can be still be improved and get cheaper. Our ability for bandwidth is going up exponentially. If I was going to take men to mars, the best use of their time would be to camp out on Phobos/orbit and teleoperate from there.

We've spent 100's of billions on manned flight and little information to show for it. That is largely because the manned programs have been almost entirely based on political objectives, not commercial or scientific. We've spent in total probably less than 10 billion on mars probes and literally have mapped and probed the entire planet at various resolutions and various wavelengths. As in situ laboratory capabilities continue to improve with nanotechnology the relevenace of bringing back samples diminishes. And if you want samples to earth it is still cheaper to do it robotically.

The next generation rovers will be much more capabable as far as speed and semiautonomous capability. I'm convinced the only reasons for manned space flight is colonization and tourism. Tourism should be a private enterprise, not a public one. We have a lot more exploration and prospecting and infrastructure building work to do before we colonize. So, for the moment I don't really support public manned space flight. It is really just sapping away money from more critical milestones towards colonization.

Manned presence has an opportunity to be bootstrapped by private companies if they are smart about marketing tourism and entertainment. That will lay real groundwork for manned presence that pays for itself and is connected to some kind of economic return. Otherwise, we will continue to waste money on flags and footprint sorties.

If NASA would lay out a real plan towards self sustaining colonies and then start the LONG development process towards that goal I would be behind it. The first stage has got to be to find where the cheapest access to resources are located. That job is done much better by teleoperated and semiautonomous robots. We really don't possess the trillions of dollars it would take to send men everywhere we need to survey and prospect. As we start to return terabytes and then petabytes of information from advanced robotic probes, virtual exploration and prospecting will become more and more possible. Witness the nascent beginnings with google mars and google moon.

1) Set some real goals like colonization.
2) Break that up into steps.
3) Accomplish each step in the cheapest way possible.