Most plans I've seen call for sub-terranian colonization of Luna or Mars. Some people want this to be the human "lifeboat" in case of a meteor strike. Guess what, we can dig subterranian "lifeboats" fueled by nuclear reactors for order of magnitude less.
As far as colonizing available real estate, Antarctica is still relatively untaken. It is pretty cold (like Mars) but it does have the benefit of a breathable atmosphere and plentiful water supply. Again, the colonization efforts would be orders of magnitude cheaper. But who wants to live in a cold/barren landscape world like Antarctica, Mars or Luna?
If you want a telescope ... build a robot. We have no need for a manned space station to take pictures, robots can do that just fine.