FF-X is my all time favourite game, so there isn't much I would change. The only thing would be if the side quests and things you needed to to to get the sigils and weapons would be a tee-e-eeny bit easier and less time-consuming. I would rather make that part a bit smaller and replace it with wider and deeper exploration of Spira and it's inhabitatants. (I know - probably quite the opposite of what most people want).