I ran across this blog entry where the comments include some great pointers on writing efficient JSF.
http://weblogs.java.net/blog/edburns/archive/2010/08/02/using-jsf-project-where-does-time-go

If you chose the Facelet aspect for your WLP project in 10.3.2, your portlets will use the “native” (i.e., WLP-only) portlet bridge rather than the “JSR-329″ (i.e., crystal ball) bridge.  In case you need to reuse your portlets in another portal framework.

I haven’t had time to try it out, but in theory one could write the .portlet file by hand and still get the best of both worlds.