* If we find life on another planet it provides a realignment for most of our world religions. That's important to several billion people. It might even create a new religion. We haven't had one of those in awhile, how exciting is that?
* If we spent $50 Billion to find algae on Enceladus we'd definitely spend 200x that to put said algae on a billionaire's plate for them to eat. That would fuel hard sciences and the economy in numerous ways, similar to how the space race gave us Nike Air shoes and the Dustbuster [1]. Like you say a human would probably never dip their toe in the water of Enceladus but we would get a lot better at drilling holes and extracting.
* We need more enemies and aliens would be great, even if they are single-celled. It would probably result in a global defense system within 50 years which would once again have several ancillary benefits for technology and warfare.
[1] https://www.jpl.nasa.gov/infographics/20-inventions-we-would...