There was definitely some significant re-editing of the score for the special edition. Notice the transitions after the cave scene and the X-wing rising from the swamp, which use the music as composed rather than cutting in the concert Imperial march. Boba Fett's departure from Bespin, allowing the music to continue to the end of the scene rather than being clumsily chopped up to end abruptly as the ship takes off. The Millennium Falcon flying away after the Avenger goes to lightspeed, extending the cue by using the previously unheard beginning section, changing the music synch to accommodate the addition of new fx. The Falcon's arrival at Bespin using more of that cue, again because of new fx. The brief high strings edited into the old mix as the Empire bombs the asteroid field are missing, as is the gong crash when Luke enters the carbon freeze chamber.

I agree that an isolated score shouldn't have dialogue or other sound mixed in when there is no music. Sometimes I enjoy the sort of 'silent film' vibe you get from the music only. Anyway, this sounds like a really interesting project. :)