I would say that somewhere just shy of 100% (maybe 95%) of all questions that don't get satisfactory answers fail to get properly answered because they were not properly asked, or lack sufficient info to make good answers possible.

In that case, simply flagging a lousy / unanswerable question as "unanswered" won't solve that problem. For that last 5% that were good but for some reason didn't get answered (5% is being generous), jingling in the CB asking for additional opinions a day or two after the thread seems to have died down is usually a more than adequate way of rekindling the thread. In fact, I would consider that perferable even for lousy questions (again, assuming sufficient time has passed), because chances are, someone in the CB will be able to explain to the OP why his question hasn't gotten a good answer yet.

On second thought, maybe the "unanswered" flag is a good idea. It will help me to filter out the lousy questions that didn't generate good answers, when I'm Super Searching for a particular topic. ;)