When I see people doing this kind of thing, I think "you must have a lot of time on your hands." Personally, I find that even after I use high-quality CPAN modules wherevere possible there is still plenty of coding to do, and the coding that's left is the part that is supplying actual value to my employer by solving their specific problem (as opposed to general problems like processing templates).

And what if there really is no template system that does what you need? Take one that's close and hack it, and submit the patches back to the maintainer. When Template Toolkit was not fast enough for us to use at eToys, we hacked it to make it much faster and then gave the code to the author. He used the ideas in it as the basis for a later release that we eventually ended up using.