I have too much respect for the art of Bratz collecting to pretend like these dolls aren't meant to be played with. They were (and are) mass-produced so keeping them in their box only supports scalper culture and hurts you.
THAT BEING SAID, when I get a new Bratz doll (esp one with lots of fun lil accessories), I keep her in the box for a rainy day. It's hard to be sad while unboxing a new lil fashion doll. I'm a 30-year-old woman, and I'll open my toys whenever I goddamn please.