If I listen to any spotify-generated playlists, it's literally the same couple of hundred songs over and over and over again. It drives me up the wall.
There's accusations they have biased their site based on how much they need to pay their artists. They've started commissioning mood music using session musicians. The only way to avoid it is to search for the exact artist/album you want to listen to and avoid all other features.
I had a suspicion it would play / recommend the same random tracks (autoplay after an album/playlist finishes) to ensure cache hits instead of needing to download songs off their servers.
I think caching is right. The shuffle mode prioritises cached songs too.