"funky caching" is what I usually try to do too on templated php-powered sites; generating static pages on access rather than on saving of data simply makes a lot more sense once you're used to it.
Although the concept of using a custom 404 php-script hadn't occured to me yet: checking if the appropriate static copy exists and the optional generating occurs in one main index.php. [via kryogenix.org]
If the amount of user types is reasonably low "funky caching" could even provide a certain "baked page" according to the rights of the user. And only "fried pages" to the Administrators.
But basically that's the idea, and it's simple, elegant and efficient, I LOVE it.
(also taking into account the lastmodified date of php-scripts and templates).