Showing (total, avg) may be a good compromise. Showing the average is an incentive for / against certain kinds of comments (i.e. against answering questions in old threads), showing both might soften that. Also, I use changes to my karma as a quick proxy for if I have more comments in any threads.

Come to think of it - a "new responses" link on the profile page could be very helpful.

Is there a reason flag isn't shown on comments until the reply page?