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I think JKR could have used Hermione being a Ravenclaw to promote inter-house relations.
You are probably right here, and maybe she realized her mistake and that's how the whole idea of creating the DA came to her. That's how the relationships built and that's how the interaction happened.
Of course she had to be super smart to be able to help Harry and Ron! They seem like average students to me, but they needed knowledge superior to their standards in order for the whole Horcrux hunt to be able in the end. How will they be able to become friends with someone who wasn't in their own House? The fact that they shared the same lessons and the same House made it possible, because they needed someone real close to them to trust, not just an acquaintance. Gryffindors sometimes shared lessons with other Houses, but I can't recall one that they shared with Ravenclaw...
Let's look at Ron, or even Percy! They don't really seem like very brave characters to me (sorry all Ron lovers out there!) but, were they chosen only because they were Weasleys? There's got to be something more to the Hat sorting you in Gryffindor than just courage, because Percy was a bookworm as much as Hermione and seemed less brave than some others!
On the other hand, being Hermione who she is, I believe she would have been a great Ravenclaw! I totally agree on that! (I have a lot of respect for that House.) I think, if given the opportunity, she would have been very proud of belonging to that House, and she would have been something beyond the best. Maybe the Sorting Hat thought that the brains aspect of her wouldn't need any further development. Maybe it thought that she could be capable of developing that aspect on her own. Maybe it did think that her bravery (which she held deep down inside) could use some development, and being part of Gryffindor would help on its improvement, just like in Neville's situation...
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I find it annoying that she seems to have a superior attitude all the time.
Yes, you're very right on this, but I think it's all part of an act. She is very haughty, but I believe it's her way to cope with being a Muggleborn. She had to prove herself and prove others that she's worth being there studying magic with all the other wizards and witches, and that was her way of doing so, through the only thing she could rely on: her brains.
Also, besides Hermione, aren't all Gryffindors a little haughty themselves too? We're all very proud of being sorted in this House, and some Gryffindors see other Houses as less worth because they're not brave enough.
I think she's a very complex character, and this discussion is definitely interesting! Thanks!