The primary use for Solaris certifications has been among Sun's IForce partners (resellers) and a few companies that require it as a standard for competence. These tests closely follow the guides for Sun's systems administration courses, so it's important to know those objectives if you won't be taking the classes.
The Solaris 10 certification exams include a healthy amount of
testing on the x86 version as well as SPARC, so you have quite a bit more study to do. I wouldn't call the exams difficult, but the subject area is extensive and the balance of questions seems (to me) a bit odd.
If nothing else, being a fully certified Systems and Network Administrator will get you a job in the reseller channel, since those companies don't always care to train their pre-sales engineers from the ground up.