I know this is already discussed here but since it's come to an end, I wanted to bring it to attention again. What some people may have forgotten is that people who know the answer to a question are not likely to look for it. It has to be brought to their attention. I totally agree that in most circumstances closing duplicates is the right choice but there are times when it's wrong. Just as an example:
How to constraint a generic to be of type enum?
Create Generic method constraining T to an Enum
In the first question I got 2 different answers (1 answer and 1 comment) which in my opinion are much better than solutions in the old questions. I think @JonSkeet for sure knew the answer to the question but it just hadn't come to his attention to answer it. So I think there should be a new option to questions:
Something like people could vote on to ask for new answers, and if a question got like 5 (or even less) votes then the question is brought to front page like a newly asked question.
Now when a duplicate is closed people could also vote on the original question to ask for new answers if it's needed.
I think this is a better option than just closing a question.