Once you start working your way through the game, you can easily leave your game overnight or however you want to gain levels with a turbo controller.
I went to bed and woke up with all the monster/fight trophies and a ton of levels.
This is all you need to do:
1) Drift a dungeon into your area and anchor it
2) Go into an easy section of it so you will not die
3) Go into the dungeon and face a wall
4) Rubberband your analog so you run into the wall and autofire the X button
Thats it. It will cut down on the platinum but you will need to grind for other things like the 1,000,000 rank and drifting dungeons but at least you will go through them much faster
First time I did it I was level 60 and I went into a dungeon that said level 3 on it. After leaving it running for about 10 hours I woke up to being level 80.