Ha! Who would have figured...
I assumed - I honestly admit - that due to the PHP coding and its parsing it was necessary to keep this line as PHP. But your method using output buffering works very well (also with the guestbook, lightbox and contact form). So to answer your original question: based on your information it is absolutely useful to convert the PHP line to a template variable. So in a next release I'll adopt this change for sure.
Don't forget to also change the 404 content variable
$ccms['content']
= file_get_contents(dirname(dirname(__FILE__)). "/content/404.php");
The adopted code now looks like the one below:
// Parse contents
function ccmsContent() {
global $link, $ccms, $cfg;
ob_start();
if($ccms['published']=='Y') {
include_once(dirname(dirname(__FILE__)). "/content/".$ccms['urlpage'].".php");
} elseif($ccms['published']=='N') {
include_once(dirname(dirname(__FILE__)). "/content/403.php");
}
$content = ob_get_contents();
ob_end_clean();
return $content;
}
$ccms['content']
= ccmsContent();
Thanks so much for the contribution

. This actually makes it possible to perhaps make the template file itself editable through the administration as well (admin only function). An idea that was suggested which I considered irrelevant because of the one remaining PHP line..
Cheers!
Xander.