I can understand the desire to close duplicate questions. However, as the site grows I suspect that there will be a lot of new users that can offer valuable responses to old questions. I worry that this new knowledge base will tend not to respond to question that are "old". Is there a better way of reviving a thread to take advantage of the knowledge in the "new" user base. Perhaps a way to reassign the question to the user that posted the duplicate question. Or if the old thread is sufficiently old (maybe three months) then close the old thread and move all the responses to the new thread. Ultimately, I am suggesting some method that will entice people answer an old question.
One thing that can help is editing the original question to make it more generalized. If a question appears to be evergreen, general, and canonical, it will get evergreen traffic. If a question appears to be something that some guy wanted to know six months ago, and he apparently already got his answer, far fewer people will care to answer.