<p>As a general rule, I think there is a difference between a full new write-up and making substantial changes.</p>

<p>Adding is extra material, citations, graphs, etc. is fine; I find it rather welcome actually! It shows that the author cared about his/her answer. On occasion I have upvoted answers that I originally thought to be "mundane" exactly because the OP took the time to make them better.</p>

<p>Completely rewriting an answer is a bit odd especially in the case people have already down/upvoted a post. I would suggest to: A. <em>add this full rewriting as a new post</em> and/or B. <em>just delete the previous post and write a new one</em>. The votes/comments around a post were given for that particular answer or at least the general gist of it; not for the complete rewrite up of it. </p>
