Give an incentive for finding duplicate questions
I've noticed that finding an exact duplicate of a question and voting to close is an act of real research on the part of the closer, and generally demonstrates better research effort than the answers do. But typically an answer will be accepted and receive a few upvotes, for more experience, when really it shouldn't have been answered in the first place. This further creates the conflict that if someone finds an exact duplicate, they are encouraged to more or less paraphrase the best answer and repost.
I would propose finding an exact duplicate and closing a question to award experience. As for details I'm not sure - only if question is closed? For each person who votes to close as an exact duplicate of the question you linked? How much rep? But seems like the right idea.