If you want to look at the current status of template usage, you could compare the templatelinks tables between wikis. Do you have a specific question in mind?
If you are hoping to look at historical trends, I'd be interested in helping you generate a dataset from the XML dumps. I've been working on a library that provides a nice, iterable, pythonic strategy for processing dumps that would let you do some parsing to extract templates. You'd need to write an island grammar to do that accurately. I've done that a few times to serve different needs, so I should be able to help with that too.