I fully agree with everything Andrew said, but would add just one other point: it depends on your career and other personal priorities.
If you don't have much intention of doing web development work, then the SCWCD is probably not a high priority.
For example, I took the SCWCD before my SCJD, but only because I had had to brush up on servlets
for teaching purposes, and thought I may as well take advantage of the knowledge while I still had it in my head. I don't use these technologies much in my day-to-day job; rather, I concentrate on core Java
development, but you never know, one day soon this might change...
Personally, I think the SCWCD exam is the easiest of the three (SCJP, SCJD and SCWCD) and if there's any chance you'll be wanting to do web development work in Java then go for it, because it's possible for someone already familiar with the technologies to polish off the exam with a few weeks' preparation.