Let me rewrite your question, and correct me if I’m misrepresenting it:

“Why should we spend resources on X instead of Y?”

Well, for this kind of question, I would prefer to choose a “high value” X and an “important” Y.

Space exploration, and science as a whole, is extremely cheap and good for humanity.

Let’s talk about other expensive “X” first:

• Unnecessary war efforts.
• ICE (if we are taking about US)
• Saving banks when they screw up on their bets.
• Incentives to coal and gas when solar is already more viable …

Maybe you started to think about it because that’s an amazing subject, and it is. That alone should be reason enough for us to want to do it. But it is not the only reason. Space exploration already gave us a lot of tech we rely on today. And still, is a very difficult field that will require more tech advancements, that will benefit us in the future.