I don't particularly care for that particular aspect of her character. Mystique isn't a rebellious child who does things out of spite. Why shouldn't she revel in her mutant-ness and explore the vast potential of her powers? It makes her seem like she thinks she has something to prove "Yeah, I walk around naked, whatcha gonna do about it HUMAN?".
It's not spite, it's pride. But yeah, what *are* you gonna do about it HOMOSAPIEN!
Like I said though. I'm interested to see how they reconcile the two very different versions of her we've seen. I mean by the end of FC you can totally see how young Xavier & Erik can become the Professor X & Magneto from the other movies, but Mystique is still missing a step to become that terminally pissed off assassin.