Dungeons?

[Veggi]

Are you able to spam Dungeons to get exp?
Or are they sole purpose for quests?

[Esper]

You can enter the dungeon as many times as you want. Just remember to reset it.
The Class EXP is suppose to be a really decent gain as long as you have a stable party to do multiple runs.

[RaineScarlet]

Once you're in the 36~40 range, you may want to spam Ulta Hall with a party a few times. You'll probably hear people saying "dino grind" or something, since the dino monsters give good exp and are fairly easy to kite/kill.