Let me put it another way: Would you rather have that $100 going to Mars for "entertainment value" or, oh say, perhaps school supplies to inner city children? Maybe it could be used to pay off the deficit? Perhaps it could go towards cancer research?
Sorry, but the idea of "well, wouldn't it be cool??" I know fascinates many geeks, but I think it's a horrible waste of our money.
If you guys want to see another moon mission, I say pass the tip jar around. You can all contribute. I don't want my money going to this project, at this point in time for our country. I'm not always opposed to this type of endeavor, but this one, at this time? What a waste.
My answer would be the same. You might value those other things more highly but I do not.
I believe that nationally challenging engineering projects pay dividends for years to come in ways that are not immediately apparent when the projects are being funded.
I believe that our future as a country will depend on the number of scientists and engineers we ultimately produce. Manned space exploration is very capital inefficient in terms of science produced BUT it's deeply engaging. It's an entry point that many current STEM workers can cite even if they're not Aerospace Engineers or working in the field.
I believe we should spend money on things that might not work simply because I think it's valuable to have a concrete national dream for the future. It shouldn't be the main thing we spend money on, it shouldn't be a top priority but the money is not a waste unless it goes entirely to contractors and produces no entertainment value.