Hmmm well that's a lot to take in but I'll start playing around with ideas to toss around here.

As for the secret room idea, sounds like it could be fun. Although making a developers room like in FFIV would be a nifty idea for maybe like halfway through the game.

Also it was FFVIII not IX that cut off all access to anything but the final dungeon at the end of the game. >.>

Also as for secret things, it doesn't all have to be special weapons or equipment, it could be extra abilities for certain characters, ability to play the different BGM's at will in a secret room, or other numbers of other little fluff things.

Also I could try and throw up a few crappy paint-job design ideas for the convention hall if no one else beats me to it later today.