This was something that was discussed briefly on UserVoice in the past but I feel that this should be another good avenue for it's discussion.
What we have seen recently is an influx of users gaining moderation capabilities for what many consider gaming the system. What I mean is that you have users who will post literally hundreds of questions, the vast majority of which will receive either negative or break-even vote totals, but the few sympathy upvotes they do receive is enough to keep their rep score climbing higher. So now we have users gaining thousands in rep even though they may have less than 10 total answers.
What I am initially suggesting is some sort of ratio between questions asked and questions answered. This would ensure that those gaining moderation capabilities are the same type of people who actually use StackOverflow (and it's sister sites) to help other users.
This suggestion could also be expanded in other ways to incorporate other metrics such as the number of high score answers vs. low score answers. This would further insure ensure that you are promoting the users who are providing good contributions to the site.