Hey Jon,
I agree with both David and Kayden--readability, emotional impact, and great content should take priority over the mechanical SEO-rewriting.
IMO, the best option here is to teach your copywriter the basics of writing with SEO considerations. Investing that time up front will save you the pain in the long-run of "re-cooking" his content. One suggestion would be to develop a checklist, or a system of some sort that helps your writer incorporate SEO best practices while writing the posts (think: synonyms for latent semantic indexing, rich anchor text, proper use of headings, etc.)
Teach a man to fish...