As one final thought regarding the Excelsior chasm - do you suppose it's possible that the ILM modelmakers took notice of the blue glowing windows on the refit that we traditionally accept as a botanical garden, and designed the chasm as an expanded feature of this, which they took to be some sort of engineering component? Just a random thought.
This is interesting as when TMP came out, I wasn't sure what those blue glowing windows were other than it was different from the other windows. It wasn't until I saw blueprints and went, ah they're for a garden. But later as I tried my hand in figuring out the internals of the engineering hull I decided to leave them as glowing bits that were part of engineering since the garden itself is never visible in any of the movies. Just IMHO.