My wish was to be able to listen to similar kind of tracks, using the genre tags. The only thing that would need to be implemented is a function where we could indicate which genre is the "neighbor" of another.
I'd bet that the system you describe already exist, but the problem, as I see it, is that genres themselves are inadequate to describe music. There are some exceptions where a whole genre is pretty homogeneous in its sound and in its themes. To my ears, rap is one example. Its sound is generally beats + samples + rhyming speech. Its themes don't vary much outside violence, misogyny, self-importance or overindulgence. Aside from rap and a few other exceptions, genres pigeon hole bands too much. Most decent artists break free from their ascribed genre, sometimes several times per album. Therefore genres are useless.
LastFM tags for Karma Police as Indie, Rock and Alternative. What does that tell you? Nothing much really. My tags for Karma Police are: Piano, Male Vocals, Melancholy, Downtempo, Beautiful, Dark. However, very few other people tag their music using adjectives, so it's almost impossible for me to use them to discover new music that other people have tagged. I can, however, use them within my own collection to create a playlist that matches the mood I'm in. I'm willing to spend a lot of time tagging tracks - its is essentially a never ending task. But this is the only way I know how to listen to music. I would go as far as saying that if my NAS broke and my backups weren't working, given a choice between recovering my music files without metadata, or the metadata without the music, I'd take the latter. You can always get the audio files again, but years of meticulous tagging can't be replaced.