Problem is that if they prune old questions, members will loss their points for asking the question and those points they received from the others who liked the question. And for those who received the "Best Answer" will loss their points. (Just thinking out loud)
A better idea might be to remind our members to check first to see if their question had been already asked.. Or, if the question looks like a duplicate then the WikiTree system could make a "warning"comment, stopping the same type question from being asked again and again. (if that is possible.) Something like it does when one tries to add a similar profile to their tree that may be already on WikiTree.
I know I am guilty of that, happened yesterday but I was in a hurry to answer someone else's request in an email and forgot where the information was lol.) A reminder would have stopped me and I would of looked for the similar question by searching the g2g forum.