I'm looking at this from the standpoint that StackOverflow is not just a means to get an answer to a question (i.e. a forum), but so much more. Isn't becoming a database of information an additional goal of SO?
I've noticed being a regular user for a few months now is that questions that have received answers are buried underneath others that haven't received enough attention. I feel that some of my questions haven't ever been looked at once they were answered, even though there might have been scope for improvement. Users who answer tend to look for unanswered questions since they have more incentive to get reputation this way. Many questions end up with one or two answers and are then shelved with no further improvements.
Obviously, all questions on SO can't cover revolutionary, ground-breaking areas, and most questions tend to be specific to the asker. For questions that deal with instructions/steps on how to perform a task, such as this one, I'd say this blog did a much better job of getting a complete, refined answer than SO (or any stack exchange site) would have ever have done.
My idea is to provide some means for the asker to request improvements to existing answers, and users get alerts to these kinds of questions with existing answers. The feature would be something like a bounty, except that it shouldn't cost the asker reputation. The main aim should be to provide the community with a fine-tuned, clear answer that has been built with multiple improvements.
Does something like this already exist?
EDIT: Bounties are fine when the asker knows that his answer can be improved. What about when the answer is posted, the asker is happy, and neither of them realizes that a better solution exists? Everyone loses out here.