First, I'd like to thank JollyDoc and the League for a fantastic story hour. This story hour has been one of the primary things drawing me back to ENWorld every day. It's been a fantastic read. Thanks for sharing, everyone - what a great story!
Second, I think high level D&D, in general, starts to become a bit of a rock-paper-scissors game. There are just too many situations for my taste where encounters are a cakewalk with the proper spell (for example Death Ward), but nearly impossible without it. The buffs are too important for success. Disjunction simply illuminates the problem by making all buffs go bye-bye. I'm generally not a fan of "rock-paper-scissors" games, because I find it limits tactics and creativity.
In addition, at high levels a significant portion of PCs' power is tied to their equipment. When that is taken away, a PC will easily function as a character of 2 or more levels lower. I don't really have a problem with that, but then you need to consider any encounter that PCs will face without equipment (such as an encounter against an opponent with access to Disjunction) as having an EL of 2 or more higher than it would otherwise have. That's a pretty extreme effect for one spell. I can't think of any other spell that can have such a dramatic impact on an encounter. I generally think high-level play would benefit from something like the following:
1. Remove or re-design most or all "immunity" spells from the game
2. Balance most encounters so that they do not require a certain foil (buff) for success. Those that do should be story considerations (werewolves and silver, for example)
3. Revise Disjunction so that it does not destroy items in the area of effect
There are plenty of opportunities to destroy equipment without Disjunction, and I think the game could benefit from even more of them! But the blanket, wide-area effect of Disjunction is simply too much for a spell that can be cast 3+ times in any given encounter.
Ok, enough of my rambling. I'm looking forward to the Savage Tide! Anyone giving odds on Demogorgon?