There are some plus sign quests that you can ignore in Mor Dhona and Idyllshire where they're either part of that expansion's relic weapon quest or a weekly quest that no one does and unless you want something like the Omnitome for glamour it can be skipped. If they only unlock and or aren't red if you're on a crafter or gathering class then feel free to do those as those help their end game. The relics from ARR and HW are mostly for show and a thing to do when you're bored as they both take a lot of time, poetics and gil.