PHP and XML/XLST/WDDX etc

I am looking for opinions and other philosophy on a couple of XML issues. I have my own opinion, but I am curious what others think and what they are doing... I am in the process of updating many of my applications to include XML/XLST/ and/or WDDX technologies. Many of my applications read a static configuration file which assigns values to variables and arrays. If we need to change something we manually edit the configuration files. In some instances, we have written web interfaces to manage these configuration files. I am in a dilemma right now between "If it ain't broke, don't fix it" and "Looking over my shoulder". I am trying to determine whether it makes more sense to use XML for maintaining configuration files. As far as content management, we use static include files or MySQL databases to store site content. I am not sure where the advantage of using XML/XLST for this functionality. Please comment.