I agree that Carbon Nanotubes have great potential for the future. But that’s the future. The specific strength needed has only dubiously been achieved in micro-materials and practically we would need about the mass of Mount Everest of this material to lift something as large as a human up. And even THEN it will only be able to slowly lift item-by-item at a rate that will not allow for quick development of space.
I’m less encouraged by the idea of a space elevator than I am of Iter.
Consider…
http://www.quicklaunchinc.com/
We have established technology that with significant but realistic investment can catapult materials into LEO. Humans remain a separate issue, but there remains much potential for revolution in that area – epically we have a separate and cheap delivery mechanism for material supplies.
The only cost limitation for such a plan is, yes, energy. Regardless of the specifics, by increasing the volume of what we send into space the price of launch will eventually approach the energy costs required to put something into orbit, most people agree with this. But… if energy suddenly became abundant by a revolutionary technology then space exploration would correspondingly become accessible.