There are probably endless ways to answer the question, but for my money she is one of the means by which a large chunk of society fulfils its needs (no matter how disapprovingly) for the trivial, the non-threatening and the trite.
I don't say this as a comment on her personality, nor do I seek to judge her. I've never met her and I certainly don't trust either media portrayals of her or her ability to use the media as a communications tool beyond the purely pictorial (witness the Larry King interview in which each of the protagonists seemed to be vying to outdo each other for the title of Most Vacuous).
Instead, I would suggest that Paris is merely a well-worn and well-accepted cliché that both the media, and the society it serves, simultaneously nourish and feed upon. In essence, Paris is a low-impact leisure pursuit. She allows us to feel superior, enthralled, titillated -- or whatever reflects our world view and our self-image relative to the world of fluff and nonsense that she typifies.
Whether we like it or not, without her we would be turning to other sources for the same kind of gratification. After all, it really isn't Paris or anything about her that holds our attention (put her profile and achievements on paper without her name attached, and would the media really give her the time of day?). And it won't be Paris for very many more years anyway. In time the media will grow tired of Paris, she will age and the fickle focus of "celebrity" obsession will alight on another sparkling vassal.
Right now she is just the package of the day. She fits the bill for what we are conventionally told is an attractive woman -- tall, thin, blonde, dubiously androgynous and gamine (almost to the point of looking worryingly young). She says little -- and even less of consequence -- yet provides endless unchallenging images of "glamour," "style" and a life well-partied. She is an antidote for the less pleasant -- albeit more substantive -- side of life that involves war, politics, budget deficits, crime, education, healthcare, environmental issues, art, literature and human achievement (yawn).
But there is a flip side to what Paris currently represents. It is the Anti-Paris, equally beloved of the media - and, like Paris, equally the focus of obsessive attention and exploitation (just for us). I mean, of course, Rosie O'Donnell.
On the surface she is everything Paris is not. Where Paris is the stereotypical feminine beauty, better known for how she looks than what she sounds like or thinks, Rosie is the antithesis of western stereotypical femininity -- she's big, loud, in your face and doesn't care much who takes exception to it. Acceptance is on her terms and if this seems threatening to some, then so be it. Rosie -- like all of us -- is defined by how she looks, but unlike Paris, her currency is infinitely more tied up in what she says, thinks and does (sometimes to whom).
Like Paris, she is loved and loathed in about equal measure. Like Paris, her unpredictability makes her good copy, with the net result that her every move / utterance is watched and reported with a tedious regularity that far outstrips its importance; both elicit the "what's she up to now?" response from anchors and reporters across networks and throughout the land.
Ultimately, neither of these people matter, but for now each is exploited in equal measure for the same purposes. Of course, it isn't a one-way street. Both Paris and Rosie know how to play the game (though Rosie has the upper hand when it comes to mastery of her relationship with the media) and both do so to the fullest extent -- which seems only fair.
But while Paris plays Tinkerbell to Rosie's Captain Hook, the media - and much of the TV-viewing, magazine-reading, Web-surfing public - remain content to have their need for trite, trivial mock-controversy satisfied. And when the two of them move on, like all good side shows, their roles will be taken by others and the audience will contentedly fill the seats.