What do you do when you find there is a duplicate question which has some answers, but none of the answers are accepted or upvoted. Do you still flag it as a duplicate even though the OP may not get satisfaction from the answers provided. Please review this question as a case to make the point. (I havent flagged it but i have commented on the duplication)
I always flag as a duplicate if the question is a duplicate. Having multiple sources for the same problem is bad. Better to have one question where we know we need help than multiple unanswered questions on the same topic. It gives us one place to bounty, edit, improve, and spread the word on.
If the answers on the duplicate look better than the original, then I flag and ask for a merge so that the better answers float to the top. If the duplicate is already closed and there are 0 score answers there I also flag and ask the 0 score answers to be removed so that autoforwarding to the original question works.
Sometimes it sucks to be duped to a question with no good answers, in that case I make a conscious effort to edit the question to improve/update it to give it another shot, or toss a bounty on it if I think it will be useful to a larger audience.