Realistically, a manned lunar station is a better bet than going straight to the asteroids. We don't really have that much experience outside Earth's magnetosphere; ISS is too low.
Plus lunar station managing lunar probes maps to Phobos landing managing Martian probes, which is a great precursor to getting back-hoes to Mars.
(Personal obsession. I've been predicting sub-soil ice since the 1980s, and almost every mystery about Mars can be answered by getting some people there with a back-hoe.)
W.