FWIW -- and it appears that pg has just implemented exactly this -- I decided to play a game with my "average" a while back, back when it was a reasonable value.
I found that it didn't improve my interaction with the site, it just changed the way that I "played the game". Not literally playing a game, but there was a clear difference in motivations for commenting.
For example: thread is more than 6 hours old? Don't comment, nobody will ever see it or upvote, so my average will get dragged down. Don't reply to any comment at the bottom of a long thread. Use short, witty comments, because those take the least amount of effort for others to upvote (I'm not good at making comments like that, though). Etc.
Interesting. What about a moving average? One that ranks you based on the last ~30 days of activity?
How about the ability to shut off karma for certain posts? One exception if it's down-voted by more than ~10pts. Then the user gets that subtracted from their score, preventing abuse when posting mean/hateful comments.
I found that it didn't improve my interaction with the site, it just changed the way that I "played the game". Not literally playing a game, but there was a clear difference in motivations for commenting.
For example: thread is more than 6 hours old? Don't comment, nobody will ever see it or upvote, so my average will get dragged down. Don't reply to any comment at the bottom of a long thread. Use short, witty comments, because those take the least amount of effort for others to upvote (I'm not good at making comments like that, though). Etc.