The following Application has been built to allow a diff of SMP Webservice Methods.
You can either compare WebService methods, compare params for a given method or Pivot the Webservices.
Click on the headings ("Compare", "Params", "Pivot") to toggle the options.
Pick a version then a webservice, repeat with a different version, this will list all Methods then a diff.
Choose a Method for a given Web Service to see the params in each version.
Pick a webservice to display a pivot of Methods for each version, toggle "UI" to add extra functionality.