Glad you're enjoying it! The game adjusts enemy levels based on your Chibits' levels, so if you upgrade your team in an unbalanced way, the game might get harder (stronger Chibits also grant more resources)... You can even finish the game without upgrading any of your Chibits!
Oh, thanks for the input! Even though I went thru the tutorial/read everything provided, I'm still trying to figure out the game mechanics! Chibits is very different from any other creature collectors on the market, so I think that's why I'm going through an adjustment period! I love it nonetheless :D