Not everyone *should* be sophisticated. It just doesn't fit with some people's personalities. In my opinion, that's ok! To me, sophistication is almost more about how a person carries herself than it is necessarily about the clothes. BUT, dressing like Cate B., Gwyneth, Audrey or Grace certainly is externally sophisticated. A bubbly person with an eclectic style might feel stifled in "sophisticated" clothing. It's all about personal style, right? That said, I do think that almost any style type can immediately add some polish by adding sophisticated elements.
I, too, however, am constantly striving to add a bit more sophistication to my style. Perhaps sophistication has something to do with refinement of style. I often feel all over the place, which makes me feel my wardrobe lacks sophistication. I try to determine my fashion personality and can never really figure it out!