I thought of doing the same as a routine treatment on the bladders. I would say pass on the Armor All, if I remember it is actually petroleum based, so it would actually cause it to dry out. From my old detailing days, the real hard-core guys always told me to pass putting that on the bumpers if you really wanted long term protection.
I would think that silicone spray might be the best.
If you get any other ideas, let me know, I really think regular treatment to those bladders would extend the life.