For purchases like that, I think a big thing is making sure you can envision a regular schedule for using it. With treadmills, that’s relatively easy, especially if you’ve already got a walking habit (although if I had the floorspace for an exercise machine, I’d probably opt for a rower). With a telescope … I have trouble with that. Which is why I (probably sensibly) haven’t bought one yet!
Ditto fancy binoculars. I’ve been getting more into birding. I’d love to get some nice big binoculars. BUT most of the times I’m looking at birds is when I’m cycling, and the “good for their size but still not great due to, well, laws of physics and optics” binoculars that I’ve got? They fit easily in the bag I’ve got on the bike. Fancy binoculars wouldn’t.
Hm, but the right fancy binoculars WOULD help a bit for stargazing … maybe I’d have known for sure if I actually saw the Galilean moons a decade back, or if I was just imagining it.