Armoury Bonus is another thing to keep in mind, when you level additional jobs from 1-50 you'll receive 100% more xp then from 51-60 it's 50% I believe.

So basically even if you ran out of quest and such to level your other jobs, doing things like FATE and leves offer double the xp you would normall get from your first job, aka a leve giving you 5k would now be 10k and FATEs that grant 20k would now be 40k for completing them on any job that isn't your highest job.