Well Russia have been doing tons of test on isolation n stuff.. Being cooped up for many many months all alone. Of course Mars colonisation would be many decades. But best to start small. (acorns oaks n all that)
Actually talking of Russia, you know theres a large chance that it won't be NASA who do this whole thing right? Bear in mind the latest bits of news on NASA have been funding cuts, them finding bacteria in California, them naming n shaming 2012 as worse science in a film, and the shuttles stopping and having to piggy back on Russia Soyuz rockets to get to ISS.
Russia have the studies on colonisation Mars trips, they have the working space program, they're kinda short on cash but I'm sure if they ask China might not be too unwilling to pony up, and there's shit loads of commercial potential for private investment.
The patents alone would be worth potentially tens of billions. If not trillions.
The propulsion technology required to get stuff shipped off fast enough to make it worthwhile would no doubt filter down to the military. The tech to build enclosed self sustained enclosure would/could allow stronger structures on earth, the ability to grow a wide variety of food on any environment on earth. Long term we'd no doubt look in to terra-forming technology which would and could allow us to do wonders for 3rd world countries and the amazon rainforest. You'd be required to make a self-sustained 'town', that would run on nothing but the materials we have on earth. If we can do that on Mars, we can do it pretty much anywhere.
Once things are more settled in the uber-rich will be able to use the now much cheaper space flights to go on exotic holidays to Mars. Thats got to be worth a bob or two. "Climb the Olympus Mons; Stand atop the highest peak in the solar system", "Romantic breaks away; No children for miles around".
Mars, in case the red hue never gave things away, is pretty Iron rich. Iron is worth quite a bit (and should they set up smelting facilities would allow to actually create more structures on the surface) So that's a bonus. Other mineable materials include Mar's 1.6% Argon content in the air. (ours is .9%)
People may say that going to MArs will cost alot. No shit. But you've got to spend money to make money. Come on US is spending shit loads on a war in the middle east for what? A few decades of oil? How very short term. Think big. Think grand. The stars the limit.