MER rovers as the first step to Mars
That's all nice if the rovers were meant to be the first step but they were not. They were part of faster-better-cheaper Goldin's way of NASA budget appropriation. And believe me, I admire JPL for persevering and doing a great job on the rovers. The scientists have to do things to survive the political neglect so that when the time comes they can do something really exciting.
But value for money - I still think not. Yes, it's cheap and yes, it's cheaper than it was thought to be as the rovers still manage to shake off enough dust to be able to function. But the return is cheap too.
And no, they are not good at finding a potential landing site for a manned mission. To survey a potential site with a rover you already must know where you want to look. To drop a couple of crawlers somewhere at random and hope they will stumble upon a great camping site it a bit naive - Mars is a big place.
As for human costs, well... how many people die daily in Iraq? People are cheap and plentiful. If you lose a few - there is always more where they came from. OK, you would want to train them to be useful, so there will be an accumulated cost.... But I guarantee, if you annouce a world-wide recruitment campaign for a Mars mission with a 10% probability of returning back safely you will have thousands of applicants in no time.
After all, some people are so bored they are happy to blow themselves up in public places, let alone fly to another planet.
Basically, I am not trying to dimish the achievement of the MER mission (showing how much can be done for a relatively modest amount of money). I am just trying to say that it is not the way forward (at least not a serious one).