No it doesn't. I'm guessing its just FF playing with the theme of crystals.

As for unused info, I've yet to read any official scenario books (Ultimania or Settei Shiryou Hen) that didn't have a bunch of stuff I felt should have been in the scenario with the possible exception of VIII. Hell, I felt half of FFX's story is in the Ultimania since it goes into details about Yu-Yevon and how the whole ritual of the Pilgrimage started as well as Sin's true purpose which is poorly explained in the game either from bad writing or poor translation.

IV's book details the family backgrounds of Cecil, Kain and Rosa which does a lot to help with the love triangle as well as explain why the three act the way they do. Did you know that Cecil and Rosa's relationship has to be kept a secret not because of Kain or Cecil high status but actually because Cecil is from an unknown family he is actually looked down upon for having common blood? Rosa's father was a dragoon and her family is actually close to Kain's. There is a whole drama in their backstory that is never explained outside of the source books.