Unlock Extended Extras Menu
Beat the game once to unlock Support Log, Theater and Unit Gallery/Sound Test.
Unlimited State Boosts for Avatar Logbook Characters
Acquire a large number of stat boosting items and gold. Save the game. Recruit the character from the logbook you wish to boost stats for. Apply as many stat boosters as you can to this unit, and update the avatar logbook for that character. Save in a new save spot (do not overwrite original save) and load older save. Repeat process until stats are maxed.