My group is currently in the City of Broken Idols and we are really enjoying the campaign so far. Having said that I am a bit leary of a couple of the last adventures, particularly Wells of Darkness (I am thinking of skipping) and Enemies of my Enemy (I am still on the fence about how to handle this one). I do like Serpents of Scuttlecove and Into the Maw though, I think they will be a big hit with my players. From what I remember of the last adventure we'll enjoy that one as well.
I remember an adventure called the Bastion of Broken Souls that I wanted to use in another campaign but never got to that level (18th) in order to use it. It involves Demogorgon though the party never faces him directly. The basic plot IIRC involves an ancient red dragon named Ashardalon that has a partially demonic heart somehow loyal to Demogorgon and slaying this dragon will give one of Demogorgon's head a chance to slay the other. I'm wondering if this plot can somehow be molded to be included in STAP?
There is a church involved called the Church of the Elements that seems like an easy swap for the Church of the Whirling Fury. I know the final encounter takes place at (or in) the Bastion of Unborn Souls in combat with the dragon. I don't recall alot of the remainder of the adventure but I plan to brush up on it over the next couple of days. Once I do that I'll post some more thoughts. If anyone is familiar with the adventure I'd welcome any thoughts on the subject.
No real advise to add, just touching on something you mentioned
It involves Demogorgon though the party never faces him directly. The basic plot IIRC involves an ancient red dragon named Ashardalon
The Wells of Darkness and god ol' Ashardalon have alot more in common then you probably know, if it is at all possible I suggest you have a read through the "Tome of Magic" and learn a bit on the Binder Base Class, or just skim the topic at the official D&D site.
After that you could check out the splat book “Dragon Magic” (page 85). Ashardalon has a few "Stats" there that are particularly interesting to Binders and maybe the Wells of Darkness once you know a little more about it.