I think that to use PHP embedded in HTML documents (the classical way, with <?php ?> tags) is effectively just using mod_php for Apache as your templating/page serving system, right?

I haven't used PHP in many many years, and even then only lightly, so forgive me if this is plain wrong. I do somewhat miss how easy it was to add a small amount of dynamic content to a page in those days without having to drastically alter how anything else worked. I used PHP in a lot of projects without ever really needing to learn it well, much the way I see a lot of web developers 'learn' SQL today. Perhaps that's why so much PHP code back then was a clusterfuck.