I'll start and then just come back to the Mars rover question.
Clearly you don't do a rover project because of the spinoffs; you do it because that's actually the only way you're going to be able to learn about our world in a way that we haven't been able to before. It's extraordinarily important to understand in the broad context what is happening on other planets.
Is there life on Mars? That's been a major initiative and focus around all of the exploration on Mars and it will continue to be. There is a lot of speculative and very interesting stuff happening. But if you actually pull off a few layers you realize, in fact, that people are looking at Mars not just because of whether there's life on Mars, but because it's actually another climate that doesn't have any asporogenic effects and is driven by some of the same things as our earth's climate is driven by, and it provides an opportunity for us to learn more about what's happening on our own planet by being able to compare and contrast.
Those are the sorts of questions you can ask only by actually going and doing this discovery science--and it is discovery. At the ultimate level you really are talking about whether Canada should be involved in discovery science or not. If you say yes, then the country should decide how much it should be involved in, and it should prioritize and make the commitments that are going to ensure it will be successful.