"One of the problems would be that the Vanguard’s orbit is very elliptical and goes through the radiation belts 2 times each orbit. So you would have a manned spacecraft passing through the radiation belt as many times as it would take to achieve rendezvous, and return to low earth orbit, or land."

No, you wouldn't use manned spacecraft- it's too expensive. A manned mission to orbit the Moon would be about the same expense and risk.
Docking with it robotically, would be about 1/2 the cost. But you are still around the cost of some orbitor/lander sent to the Moon or Mars.
Plus, it's possible that radiation dose to crew could around level as if a crew were sent to Mars.