If you're willing to take liberties on your definition of RPG, there's Disgaea DS and The World Ends With You.
Disgaea is a strategy RPG which gives you tons of freedom in stat-maximizing. You can level your characters up to level 9999, optimize their stats well into the 7 digit range. You can even customize your weapons and strengthen them by leveling them up. This game will make you spend dozens of hours, highly recommended if you enjoy Pokemon.
TWEWY, on the other hand, is an action RPG. While there isn't that much emphasis on stats, there's a lot of post-game collecting and optimizing. It's pretty addictive.