And you can't rely on automatic classifications either. But then music providers don't give you proper info for the music they provide. It's a circular problem.
And then it's a social problem, too. You may want to listen to music that other people that listen to your music do... But then you might not want to do that.
It's a mess.
If Spotify could increase and sustain the catalogue then I'm pretty sure this would work. But it feels like the catalogue is smaller, churns more, and isn't as enriched in meta-data or listener behaviour to make it work yet. A network problem more than a technical one.
Blogs, discogs and national radio actually work a lot better for me for discovery, simply because, as you say, Spotify may not even have the input data in order to then help me discover better music. Thing is, I'm not sure there is a desire (perhaps economically driven) to improve that catalogue as they would need to.