I suppose it might be the case that a new user is trying to gain reputation by re-asking old questions, but that aside, what is the policy on re-asking old, unanswered questions?
I understand that there is value in bringing it to the attention of the community so that it might finally be answered, but at the same time, you're creating a duplicate question. I think that upvoting/commenting on the original question to bring it to the top of the queue might be a better solution, unless there is something different about the new question (such as the inclusion of the asker's thoughts on the matter?).
Is there any official policy in place regarding this situation? I know that duplicate questions in which the original has an upvoted answer are closed, but I am not aware of anything pertaining to unanswered questions.