There isn't just "good metric" in vacuum - it was a good metric of exactly the popularity that you mentioned. But stars becoming an object of desire is what killed it for that purpose. Perhaps now they are a "good metric" of combined interest and investment in the project, but what they're measuring is just not useful anymore.

Yeah, I'd agree with this. I always thought of a star indicating only that a person (or account, generally) had an active interest in another project, either through being directly related or just from curiosity. Which can sort of work as a proxy for interesting, important or active, but not accurately.