Slightly off-topic, but why wouldn't you want to level all jobs? You can only truly master your job(s) if you're fully aware of the relationship with others. I'm not saying specialise in all jobs, unless you have a good deal of spare time, but levelling them up and completing their quests isn't a huge bother.
Personally though, the quest-lore is the main driver for me to level jobs, as I found trying to get a group for battles and dungeons very hard.
