My idea for having relic users contribute to new players:

Atma: Give a x% drop increase for each pre-50 player participating in the FATE. Level appropriate players may contribute or players too high may not at all.
Books: Give X amount of tomes if a new player accomplishes a dungeon for the first time when you do your book.
Alexandrite: For FATEs, same things as Atma (very helpful for helping players level new jobs in Cortheas, or bring new life into Bluefog FATES back in 2.0. Also increase the amount of tomes if a new player clear content the first time while doing Expert Roulette.
Lights: Increase lights by one more steps or by a multiplier if a new person clears content for the first time.
Zodiac: Increase drop rate by x% for each item involved.