That's seems a very narrow definition of scientific benefit, or you and I differ on what's beneficial for science.
The discovery of water and bodies of water on Mars, in my opinion, is benefical to the study of Earth geology. Because it raises the question, why did Mars lose its water, and by extension why did it lose its atmosphere. Could something similar happen here on earth?
Considering what we're learning about the two planets shifting magentic field, I'd say study of Mars is fairly pertinent.
I'm not arguing about studying Mars or space in general. I am with you that far. Completely.
But what are our priorities? Fight terrorism? Provide Social Security benefits? Put people on the moon? Cut taxes? Redevelop inter-city areas?
Maybe you want to do it all. I see it like a family budget. In that context, the manned space flights go into the garbage bin. We can't do everything. Maybe you can; I cannot.