The thing is Johnny, you started off adamantly stating that any song whose lyrics are not transparent has failed. I sense you're trying to backtrack from that now. I think also some folks are wading in strong as your original post had a touch of didacticism about it, which can come across as arrogant.
There's no single definition of a successful lyric - if there was, songwriting would be all craft and no art. Personally, my lyrics exist almost entirely in the opaque realm, and that's the way I like it. The songs rely on creating an emotional response in the listener. Whether listeners objectively understand or can analyse that response is irrelevant IMO.