I'll throw in a less experienced view on the topic. I'm working on my SCWCD right now because it will help me on my current job. I am a junior member of a J2EE web development team.
On the previous phase (after my
SCJP) I worked on the model classes. I have several years of
Java experience before I got my SCJP but I found that I learned many things about how Java really works that helped me a great deal.
Now I'm working on the UI layer of our app, using Struts. I have found the same as before - Struts is much easier to understand because of the things I have learned in my studies for SCWCD.
For example, I can look at all those Struts tags and know what the compiled
JSP servlet class will look like. I can look at all the interaction of the ActionServlet and ActionForm and understand how all that communication is being implemented under the covers. And I know how much work would be required to do all that traffic cop work if Struts wasn't doing it.
So in summary, I highly recommend studying for the SCWCD prior to learning Struts or another framework. Walk before you run.