The quality of questions is the main problem, yes. May be they can be upvoted or downvoted, so they would appear more or less frequently?
This is a great concept - giving each question a score and allowing it to gain/lose exposure based on it, similar to HN/Reddit.
Or, and while we're at it — location filters for location-based questions would be the greatest (although much more hard to implement) feature. I don't want to answer someone's question about his homework, clearly directed for his friends, but I would gladly give advice to a tourist who found himself in a place I know.