If I had to choose, I'd take the threadstarter's avatar over having post icons. But I would like an Admin option to turn on post icons anyway. Or maybe it would just be featuritis. I'm undecided now.
I love this idea as it was what I was thinking then I read you suggesting it... I would like to see read threads have the poster avatar just slightly faded sorta 0.8 just so it is noticeable.