Level capped.

What do?

What's the carrot? Grind and grind and grind and grind some more and eventually maybe get a 13* or two to sell?

Level more classes for permanent class boosts, go for class EX-Cubes for extra skill points, prepare for future content, etc. And depending on how many you want to play, skill rings for each class. Affixing weapons/units is also the game's scalability meseta sink.

Ultimate Quest farm for Gix and Nemesis (Naverius) / Slave (Lillipa) weapon drops.

Max out your class cube quest for additional skill points. This was a requirement for being able to progress to level 80 when the cap increased on JP but I'm not sure if it will be mandatory for NA.

Level more classes for the title boosts if you feel like it.