Scientifically, there's very little a manned mission can accomplish that an unmanned cannot - and for each manned mission, you can produce like 5-10 unmanned missions.
I say, let private companies battle it out. This is the only way rapid commercialization and real progress will be achievable.
NASA has been a pretty big failure in terms of manned activities in the last decades - seems to me like a result of stagnation of bureaucracy. There's no excuse why the backbone of the US space program is a vessel designed in the 1970's (Shuttle) with a dubious safety record. Surely the private sector can do better than that?