Admittedly, the detail about the teacher's past isn't overtly relevant to the original album version. The reason "Teacher, Teacher" ended up being ditched is for that very reason. All that really matters for the album (and the movie really) is that the teacher is a scumbag and his actions are a major point in driving Pink into himself.
And I don't think the "Conqueror Worm" is necessarily something we're supposed to pick up on either, assuming that's what Waters was going for. The worms just mean mental decay. It's not a very deep metaphor, but it's functional. And Waters admits to them being cut back from the album a fair bit, but the line on "Hey You" and all of "Waiting for the Worms" make the point well enough.
I'd like a source on him saying he hates mystery, but from his lyrics alone I'd agree that subtlety isn't exactly his driving force on his albums for sure.