We've done well with robot explorers, and I believe that is always the best "first encounter" with new environments. However, a human on mars could do more than a robot (at least the ones currently designed) could. For one, get unstuck. Perhaps clean/empty a testing container (soil sampler currently has only 6(?) testing chambers).
Of course, while we're still squabbling over who has to foot the bill for exploration and scientific progress, progress will be slow indeed. Just think of the progress that would be made if we knew, 100%, that a rock would smash Earth in 30 years. I guarantee one of two things would happen: 1) We invent/build some tech that will blow up/push the rock, regardless of global cost (yes, a global effort. funny huh?) or 2) the very wealthy would pool their money to life-boat themselves off until it is safe. (yes, I know, it sounds awefully 2012ish, but which is most probable?)
I for one vote for the original plan. Heavy lifters to get the crap up in the debris field known as LEO, construct the ship there, then ferry our happy, curious selves to wherever our propulsion can get us. Perhaps we'll have something akin to warp drives by the time those in charge finally figure it out. (I'll let you figure out which is more likely to happen first)