I think the impetus of expansion into space should be driven by autonomous, partial- or full-closure autoreplicators, whether macro (minimechanics and MEMS) or nano (drextech). For this, manned spaceflight is but a distraction, and a possible resource drain.
What is necessary is cheap delivery to LEO, which is primarily pushed by conventional satellite industry, and parallel terrestrial research in space simulators for the development of lunar and asteroid industrial processes. This might eventually require microgravity experiments, but this is nothing that cannot be handled by automation/unmanned flight. I realize that the state of the art in automation/robotics is not exactly awe-inspiring, but this should not be glossed over by relying on monkey power. If there are deficits, let's address them now, since we *will* have to deal with them later.
After the transport structure and habitats are constructed the humans could follow (if there are still any around, that is).
Imho, manned spaceflight is only tolerable as long as it advances the state of the art/mobilizes the resources otherwise wasted elsewhere.
If this sounds like pompous foolishness, I'd like to hear counterarguments.
> Is this latter mission for ISS really viable in the time before, say, 2025 or
> so? I know there's been quite a bit of talk lately about "space tourism",
> but I'm skeptical of this as a viable economic development within the next 25
> years (after a fairly advanced nanotechnology is developed, yes). I'd be
> especially curious to hear the thoughts of younger folks who may well not be
> infected so strongly with the "space station meme".