1.Armoury Chest
i think it would be a great feature to turn the armoury chest into a collectible chest for all unique gear. A box with the picture of the item and a tick down in one corner to say you've collected that unique item. collected sets of items such as all bards darklight armour could reward you with gil and tomes. single sets could reward you with gil and company seals.
i think this would encourage people to replay old dungeons in order to try and collect all the gear available as well and cause people to roll on drops. nowadays I'll be in a dungeon and about 1/3rd of the time the item will be passed on by every player. it would certainly encourage me to go back and do old dungeons in order to get all items ticked off and collected.