I have a doubt: should I install Spring dependencies using the ant build included in jbossws-cxf distribution, or can I just copy the Spring modules of my application?
You can use the spring version you want as long as the org.springframework.spring module is properly created (either manually or through the jbossws build).
Still, if the first hypotesis stands, why should I keep on using the JBossWS implementation, instead of disabling it, and provide my own preferred implementation in the application?
What are the advantages of using JBossWS?
It's basically a matter of deciding if you want a web application that has ws functionalities in it thanks to the jaxws impl embedded in it, or if you want a full javaee application. The latter, using the jbossws / cxf libs on the server, offer proper integration of with the AS internals, support for jcp specs not covered by cxf (e.g. JSR 109), etc.