What's the point?
The question is not whether mannned flights to Mars, the Moon, or a Near Earth Object are possible: they are.
The question is "What would be the benefit from any of them?"
My view is that the benefit of early detection of a potential impactor easily justifies the construction of a man tended lunar observatory on a cost/benefit basis. The yields from the other two projects would be far, far less.
For an architecture using the current generation of launch vehicles for the construction of a man tended lunar observatory, see
http://www.geocities.com/epgrondine
EP