It's not like the money disappears to Mars.

It creates high-tech jobs here, gets spent here, and we learn things about our universe at a ridiculously low cost, overall. It's about discovery, and we don't know precisely what we'll discover.

After all, the electron originally was such a discovery, and was largely considered useless by the pundits of the time. Yet now, look around you: a whole world of electronics.

The money for space exploration gets spent right here on Earth.