The Levee is a really interesting AP. I'm honestly not sure how good / playable it is *as an AP* -- with all respect to Mr. Pett, it reads more like a super sandboxy collection of high concepts than an AP as such. If I ever ran it, I suspect I'd have to modify the hell out of it to make it coherent and playable. But it's very interesting -- there are a lot of cool ideas and no shortage of well developed NPCs and weird, intriguing situations. So I'm mildly surprised to see that no group ever stuck with it.
I agree with you that this is a very interesting AP and like you, I am surprised to find so little support for it online, no community created content, no journals, no long-lasting PBP, not a lot to go by for anyone who'd like to tackle this AP and wants to pick the brain of others who've played through it.
I also agree that preparing this AP for play requires modifying the hell out of it, which is exactly what I've been doing for the last couple of months. My setting will be Ustalav in Golarion, the alternate Between dimension becomes the Dimension of Dreams. I'm definitely toning down the extreme horror element from the original AP, I'm inserting ideas from other adventures, like Strange Aeons and Ravenloft. I'm also using the D&D 5E ruleset, because I want to try out a slightly simpler system, instead of the increased technicality of Pathfinder 2E.
So, are there any others out there who have played through this AP and who want to share their experience? I'd surely be interested.