I think stackoverflow is more than just sum of it parts. Solutions presented there are not just provided by experts, they are reviewed by experts, and if someone has a better solution, it has a really high chance to boil to the top. Portion of experts will recognize that and adopt superior solution. This will keep driving code quality and standards of participants up.

Or at least so my reasoning goes. So to answer the question, I believe it had done much more than that - stackoverflow drove people to improve their technical knowledge, and that is priceless.