I basically see voting as recommending an answer to a user where the question has been unanswered. Once the user accepts and answer, I don't see much reason to vote. Why participate if the contest is over. Perhaps it is a wrong headed view about what voting means but I doubt I'm alone in this view.

I've updated my answers to give more specifics. However, I still think that duplicate content lowers user engagement. If you could funnel all of the questions about a specific issue into a great Q&A, I would be more likely to vote on that great information.