If we're using stars, why not base stars on comment percentile? Every night at midnight, take all the comment scores for the last week, and determine the 90th, 70th, 50th, and 30th percentiles. So every comment in the top 10% gets 5 stars, every comment in the top 30% but not in the top 10% has 4 stars, etc.
Also, I think we should switch it up so that comments are dimmed at more like -1 or -2. Otherwise, if the first vote is a downvote, people might overlook an otherwise decent (or controversial) comment.