I was just using your words. A lot of the the things you've been saying about ENFP's describe Gwen perfectly. Gwen never goes for the "Pow!" effect with her fashion style- whatever she's wearing always seems to be reflecting her current state and mood, especially in her music videos. She isn't exactly 'grounded' all the time, either. Looking at her, I notice that she seems to have that faraway, N-look in her eyes half the time whenever I see her. And, even though N's don't hold a monopoly on finding the meaning behind things, there's a level of depth that gives them away.
ESFP's don't like theory and abstraction in general, they're more detail-oriented and practical. Gwen isn't like that at all. If you ask her for the details, such as her work-out routine, she won't vividly describe the details the way an ESFP would. She'll say "Uh, I don't know, I do sit-ups!" She's way too metaphorical and big-picture oriented with the way she talks to be an S.
And no, I'm not saying that any of that's a good or bad thing, in case you're going to take any of what I'm saying to insuate that I dislike or having anything against ESFP's. I'm not denying that they're awesome people, I'm just saying that there's no way in hell that Gwen is anything like one of them