We've already been there twice. The ISS is just a precursor to man living on the moon for longer periods of time, which will be the precursor to man living on Mars.
No, the ISS was a stop-gap to give the shuttles somewhere to go and to keep the Russians from disbanding thier program entirely. We haven't learned anything from the ISS that we didn't learn on Mir. Anymoney that would be spent on future manned space shuttle trips would be better deposited towards a permanent moon presence now. In otherwords, stopp all manned flights for the next five years and spend the money on that instead.