I've had similar thoughts. I think it would be possible to create a web app that will take the XML file as input and then output the wiki template text so that you could cut and paste into the wiki source.I've been looking at a .dnd4e file. This is just a huge .xml file. I'm quite sure there is a way to read it and transform it into a L4W template file. Sure, there will be a few missing information, like power description, but all the math part should be easy to get out of it.
I think there is some work that could be done to clean up the wiki templates too.