Close flyby objects are almost inevitably poor rendezvous objects because their relative velocity to Earth is usually prohibitively high (it isn't distance you need to worry about but delta v); but see http://www.aas.org/~dps/decadal/whitepapers/jones_120701.doc, which is an official NASA decadal plan document on the concept (not some daft space cadet sf).

The important thing here is that scientists have discovered a couple of NEO trajectories which allow return flight times of around six months & delta vs less than that required by the most fuel efficient Lunar landers; & while there aren't any currently convenient targets in this list, the potential for finding new targets of this kind is pretty good. IF a good rack of these trajectories can be collected - probably so that there is are annual launch opportunities or better - the idea of reinforcing a cloned Mir/ISS-class component for radiation shielding & launching it on a cheap NEO rendezvous mission actually makes some sense as a first test of a sustainable manned exploration program.

Frankly: if we had the trajectories, we could do it now - which is not something you could say of the Lunar & especially Martian alternatives.

Robert