First I disagree with you as to the probability and desirability of putting men on Mars, BUT leaving that aside for the moment, If the choice comes down to my paying for it or the Chinese paying for it, then let the Chinese waste their money.
Mars consists, unsurprisingly, of rocks and dirt. How much more taxpayer money should we spend to confirm this basic observation?
There is a little thing called the "Periodic Table of Elements" that dictates what we will find any place in the universe. (Hint - the answer will always be rocks and dirt as dictated by the interactions of the elements in the periodic table)
You disagree with me about the desirability? I did not touch on that aspect, only the inevitability. I honestly believe that homo sapiens will spread to the planets of our system and beyond. Blame Heinlein, Nevin, Roddenberry, Asimov, Clarke, Von Braun, and Kubrick for planting such beliefs in my head.
As for who is going to pay for it? Well, I can think of several ways to pay for it without forcing taxpayers to foot the bill. As long as NASA is around, they will continue to justify their existence and, in the process, do some good technology development.
Hint--the idea isn't to find minerals or rocks. It is to explore a new world for mankind to conquer. The question is who is going to explore it and what kind of society will evolve from this exploration.
Bonus Hint--Look at how exploration and settlement evolved in the Western hemisphere. Spain and Portugal basically conquered and settled South America. North of the Rio Grande was colonized by the English and the French and later other Northern Europeans. Judge the result for yourself.
Curiosity is looking for water.