I've used SOAP (nusoap for PHP) and I've used XML-RPC for exchanging data between websites. In my experience I feel that the XML-RPC route is handsdown the faster of the two methods. Which got me to wondering what your thoughts/experiences are.
I believe you are correct. For all of my needs, I've only had to handle simple db queries and pass the result sets back. But that being said. The nusphere.php file is a VERY large file to load. I have to believe that one could write a similar SOAP server and SOAP client that wouldn't require such a large file.