The series is pretty clear about the actual contents of altered states being largely garbage, so your observation and skepticism regarding "amazing ideas which they somehow can never write down and keep for later" is exactly in line with some of what's being discussed there, not contrary to it.
However, here is 1 concrete example from my own life.
I had a friend who was extremely manipulative and would lie to me constantly to get sympathy or compliment me to ingratitude himself. He would steal from me,but most of the time he didn't need to because he knew I was generous and I would give him basically anything he asked for. Cause we were "friends"
I took acid, and watched him come over to my house and completely commandeer a party. I just sat watching his mannerisms. How he interacted with people. It became so clear immediately that he was an absolute fucking sociopath. When I sobered up I booted him out of my life for the better.
And this was not a case of me reading things into him that weren't there. When I sobered up I talked to all my friends and they were like "yeah that guys a fucking bastard we all wondered why you put up with him"
Something about the trip allowed me to perceive him in a way that I could not or would not have otherwise. I saw right through his flattery and fake charm.
Weird example, but in my life it's the only concrete example of a positive change from psychedelics.
Now I've got about a million negative stories, but there's a positive one for ya.