A '4' on AWA actually isn't that bad--I know plenty of people who scored a '4' and were accepted to top MBA programs. More importantly, you did really well on your actual GMAT!

You might want to call your test center, but I think that they do not do re-scorings of tests anymore. Even if you did, I don't think it's worth doing just for your AWA, since it's okay.

With regard to your question about how much b-schools weigh your AWA. From what I know, they don't emphasize it too much. They weigh the writing in your application essays far more than they do the AWAs. At the extreme, they might use your AWA as an example of another writing sample. Again though, I wouldn't worry about this too much.

Hope this helps, best of luck!