Space exploration can and has provided benefits that are used back here on Earth. A broader understanding of what is around us, information gained that can be re-applied at home, Tang, etc…….
I’m not sure what specifically sending a manned mission to Mars will provide that sending robots cannot. The physics required to get a person to Mars and back in a healthy manner are far more daunting than sending a robot. Some say it is human nature to explore and I agree. Where the limits to that render it counterproductive is up for debate. Each mission carries risk and reward. Manned missions cost more thus have more risk for similar potential reward. The further we go, the more this is pronounced.
SETI and the like is where the real waste exists since intelligent life in the galaxy/universe has essentially been ruled out mathematically already. Thankfully the percentage of money spent on that crap is actually pretty low, but every penny is a wasted penny.
If I were in charge of everything, I wouldn’t be too far off what we’re doing but probably nix any manned Mars stuff for the foreseeable future. The ultimate goal would be to explore the galaxy and expand our domain, but not by transporting blobs of flesh around at enormous cost with little chance of success. It would be small dna samples on small self replicating robots. We don’t have that technology yet, but it will certainly be here before any Star Trek mumbo jumbo.