> Why will it so often not display any results at all, even for system apps like Safari or Terminal?

I've experienced this too, even after giving spotlight multiple shots months apart. For your sanity, I say just stop using spotlight. Don't let Apple steal your valuable waking hours with their crap QA.

I’ve had issues like that in the past, had to clear the cache for the spotlight index or something like that. Fixed it right away. Not sure if you’re facing the same issue.