I haven't personally used it, but I do know that ListenBrainz offers a Last.FM-esque experience, and I see it does have a "similar artists" section. I'm in a similar boat as you though. Most of the Spotify-generated stuff is just repeats of songs I've already liked or just generic songs.
I've been diving into the past about artists I've been meaning to check out and also using Rate Your Music to stay semi-conscious of what's popular today.