Absolutely worth it. We wont fill the galaxy filled with life because the galaxy is huge and we are but one tiny tiny portion of it. For us to survive and do anything impressive takes all of human ingenuity.
Also those two items aren't mutually exclusive. Both can and should happen in tandem. Anyone arguing otherwise is just a mentally lazy person.
Whenever you have two goals competing for the same resources, you need to prioritize. I'm for preserving life on Earth first, and spreading it to other places as a distant second.
Again you aren't competing for the same resources. Our global resources are plenty. You are unnecessarily making a dichotomy.
Of course preservation of life on our planet should be paramount. We can also pursue space travel. Space travel research isn't whats killing our planet.
Also those two items aren't mutually exclusive. Both can and should happen in tandem. Anyone arguing otherwise is just a mentally lazy person.