I feel such comments when presented like news.yc votes or FriendFeed likes add more value because of their conciseness.

  (define (value conversation-element)
    (- (benefit conversation-element)
       (cost conversation-element)))

  (define (cost conversation-element)
    (- (conciseness conversation-element)))

I'll leave the definition of (benefit conversation-element) as an exercise for the reader.