Excellent write-up. I've seen all of these, some several times. Purple Rain was a snoozefest. I saw Sgt Peppers when it came out and I didn't love it at the time, perhaps it has matured with age...?

I'm going to suggest a movie you might not know, even though it breaks your rules - it's more of a documentary.

A Blind Eye Sees All is about the Butthole Surfers, and it just gets better and better as it goes. Gibby has some inspired flights of free association - I had a girlfriend who had memorized one of his rants.

This great review says more than I can:

The truth about the Etruscans, the Bolivians, the Artesians and the Wallhonklers for example, or the Chinese men tied to walls showing worm movies through their penises into the air “in apparent disgruntle and dismay”. Some of the images Gibby grasps from his addled stream of consciousness are stunningly odd, drawing out an LSD epistemology which includes the Fartholes who “had VW buses that they had designed like they were cathedrals of GOD!”

You can see a moderate-quality version on YouTube.