Good to hear of your successes !
I agree with much of what you say here and your experiences about gluten reduction "potentially" impacting Auto-immune problems and making POIS symptoms worse. Similar with dairy and the sinus related issues of POIS.
When I eliminated (out and out) dairy products as much as possible about 15 years ago, my serious headaches with POIS reduced (although I still to this day need the daily cortisone spray).
Over a year ago, when I also started reducing gluten and taking less wheat, I think I also noticed some improvements - in particular awakening in the mornings didn't feel like 'having been run over by a bus' in the night.
As I'm older, the 4-5 times a day isn't as much of a problem as it was in my 20's.
I think your behavioural change related suggestions below are worth trying. Hard to be disciplined to follow, because as you feel a bit better, you naturally want the trigger stuff.
However, POIS is there, but potentially this is about what makes things worse or what reduces and improves the fall-out of POIS. Not sure these strategies will actually cure chronic POIS.
Good news to hear you have found good relief however.
Hopefully the good Dr. K & team can look at this issue in terms of the Vagal nerve connection with digestion also. I think others may have mentioned this. A long wait, but hopefully it'll all come together for us in 2014.
Here's an article that I saw and posted some months back about this (autoimmune and gut problems).
http://www.mindbodygreen.com/0-8843/10-signs-you-have-an-autoimmune-disease-how-to-reverse-it.html