Suggest “Questions you may have an answer to”
I'm just thinking it might be good to place a "you might know the answer to this question" block on some places. The block will contain the link & title of the question, how many person already answer it and a simple answer form.
The question pushed to that block will be determined from user tags, browse, ask and answer history. That way, it'll increase the ability to check on duplicate or similar question. This time, helped by real human (not algorithm based).
This will also encourage more people to share their knowledge by answering the question the might already know. I believe there are a lot of smart and knowledgeable user on SA which should be able to answer some question appearing on SE. But they just don't have time (or at least don't have any willing) to check on the unanswered page. They intend to just use SA to ask his/her own question.
I think this will build better engagement to SE.