Rasto,
It is possible to create separate projects for different JBoss Tools/WTP servers. You also have to create different projects for different versions of servers.
Source Lookup has some additional features:
- adds source jars automatically without any user intervention
- adds source jars for different servers: JBoss AS 6.1, JBoss AS 7.x, EAP 6.x ,GlassFish, Tomcat, that is, any server having mavenized jars
- works when using plain, non-mavenized Java projects
- works even with mavenized jars within a plugin (org.eclipse.m2e.maven.runtime, for instance) when launching Eclipse as PDE Runtime