Having been born in 1982, I guess I’m just outside that “sweet spot demographic” you mentioned. I’m also a very wrong example in terms of cultural background (Harry Potter didn’t arrive into my life until much later in the frenzy) but I love Harry Potter.
Beyond it’s modernly classical way of using language — something that pretty much equals the innovativeness of Tolkien, for example, albeit in today’s context, which I guess was the main source of the sneers — and, in my opinion, inspired literary devices that point well beyond “children’s fiction” (the anagram being the key in Chamber of Secrets in particular is something that goes way above the heads of the audience to which we normally assign Harry Potter).
But beyond its own merits, I think Harry Potter revitalized our culture of reading, for which we cannot be thankful enough. I’m somewhat decidedly ignorant on why or how we get new generations, whose main source of entertainment isn’t necessarily the written word, to dive into reading. As long as they read, and buy books, and try new things, I’m good. I know people sneer at pulp, and I myself can’t stand reading Dan Brown, Stephanie Meyer, or any of the others like them. I do try from time to time. But regardless whether they or Rowling can write (and it’s my opinion that Rowling can, and Ms Meyer and Mr Brown can not) in this particular context their ability to get people reading is far more important.
And that effect is hardly temporary. The generation — somewhat mine, too — that received the full force of this reading renaissance has grown up to be now the major demographic that spends money. And they grew up as people who read. Their children will grow up with parents who read. It may lessen over time, but the chain reaction of generations to come who are embedded in a literary culture, mixed with generations who grow up embedded in a multi-media culture, will reverberate for a long time.