You dont need to know as much java, so in a way you could regard it as a stepping stone.
It will help you to get used to Suns tests, which can sometimes be counterintuitive ("which 2 of the following are not true", rather than which are, etc.).
It is a much broader exam, whereas SCJP is about syntax and low level bit calculations, SCJA is a higher level qualification, dealing with how java should be used, when J2EE (or whatever sun is now calling it, JEE5?) is appropriate etc.