For posts that have been answered, it would be nice to see a "Followup" section (just below the original question text section) where I can put a followup narrative about how I used the 'checked' answer to completely solve my issue. Right now, if I want to post followup information I need to edit the original question and it doesn't look that nice when you do it that way. Also, you could add badges for being a good user for following up and adding more info after the question is answered.
I usually just put an EDIT block in as you mentioned. I think this is a good way to do it, because many times there are multiple EDITs to be added in as an issue is worked, and input given and received.