It never occurred to me before, but it'd be great for GitHub et al to have a way to leave kudos and thank-you notes. As things stand, the only affordances are for leaving issues and complaints, so it's not surprising that that's what get left.
(A really cheeky issue tracker could have this built in as issue 0.)
Thank you issues while clutter would be my favourite off topic issue to close.
I don't think you can generalize here; it's like Twitter, where some people use Likes to remember all-time favourites and some people use them as an "I've read this" checkbox.
I might Star e.g. Postgres (yeah, I know, not their official repo) because someone told me that it's an example of good, elegant code, and I would like to study it. But that doesn't mean that I'm a Postgres user, let alone an adoring fan. I'm starring the code.
Let me pile on btw: great tool!