If your goal is science send robots, if your goal is the eventual colonization of Mars still only send robots for now, if your goal is adventure send people.
Adventure is kind of a selfish goal, considering that only one or two humans get to enjoy the experience. All those resources and manpower is a waste if the rest of humanity doesn't benefit from it.
It's perfectly OK for a rich billionaire to do it...but NASA's focus should be science and not pleasure, I feel.
