I've done this with a lot of the game's dialogue. There are some wonderful lines of text in the game that were cut for some reason, like Ward and Kiros teasing Laguna about the "Piano Lady" before they visit the club. Square also cut what's probably Squall's best line in the entire game (it's at the end of the trailer I'm working on for the VO project).
I noticed the unused dorm rooms. The problem with these is they don't support all the costumes, so I'd have to script all the areas that would jump you there if I wanted to use them at all. They would be cool to use, but it's way too much work for a little polish. If anything, I'll only slip them into a single scene.
Also, I plan to use the "Balamb Garden gets hit by missiles" FMV that's on disc 2. Maybe it will play if the party dies in the MD levels.