I think I've figured out the regex to search/replace those <div id=...> things out:
Search for: <(div id="\S+?") (class="para-normal">.+?)(<\/div>)
Replace with: <p \2</p>
"Wrap" and "Dot All" are checked in the Search dialog. That looks for the first occurrence of:
<div id=blahblahblah class="para-normal">blahblahblah_until_it_reaches</div>
it replaces that with:
<p class="para-normal">blahblahblah</p>
I'd reduced all the paragraph styles down to that para-normal and paracenter (one of mine). I just had to do another run with paracenter in the place of para-normal.
That appears to have worked. Next, I've got to get rid of the <br ....> things that are at the end of most paragraphs.