Tim,
Good answer!
So - of course I'm thinking now that you could setup OASIS CAM templates with XPath expressions - and then use CAMV engine to help you do test automation.
The article here explains how IBM did this recently for their OAGi BOD based messages - and contains the necessary Java code and library files to run CAMV.
Should be a good fit to setup in a lab environment - and with a bit of front ending could be a web service test facility also - that reports back to the caller in either HTML or XML the results of the test (post process the test results using xslt - there is a sample xslt in the download).
Thanks, DW