Hmm. I think Avril was supposed to be "anti-image", which in itself is an image that can be just as manufactured as any other image. And now that Avril dyes her hair blonde, likes to curl it, and wear more feminine clothes, she is not the popular artist she once was. I think if you are too focused on one image (like her signature straight hair, tomboy clothes, etc.) then a departure from this may cause a career downfall as the artist may have lost a lot of what the public identify with. (Though of course this isn't always the case, just look at Madonna.)
In contrast, Vanessa has that cool vintage look going, but she isn't limited to one look. And I like the way she is sexy in a subtle way, as opposed to a "look-at-me" kind of way. (Though, I guess I'm not the best judge of sexiness as I don't rate chicks.) I think V is a good role model in that way- she shows it is sexier to feel confident in your own skin rather than trying to be sexy by revealing too much skin.