Whether you move on to the higher WSET levels, seems to me, to depend on what you want to do in wine and how determined you are. It's a tough one to call.
I started out with a Dutch wine certificate (similar to the WSET Advanced Certificate before it became a touch harder). That was just to learn more about wine as a serious hobby but the bug hit me during the course of that. A bit later, Holland's sole Master of Wine started up WSET courses here in Holland (I am an American living in Holland, by the way) so I jumped at this opportunity with the hope someday of working in wine, not knowing what but determined to at least try. Consequently, almost three years ago, I started the Diploma Course (it was required to take the Advanced Certificate test and get that certification first, which I did). The Diploma Course turns out to be hugely difficult - it is completely oriented to professionals; whereas even the Advanced WSET course is still for serious hobbyists, the Diploma Course is completely for trade folks. Night and day kind of stuff. It is very difficult to pass the Diploma Course if you are not already in the trade, just given the amount of tasting and business expertise it involves/assumes. I am only one of three folks who are not in the wine business and am finding it very difficult. However, the good news is that, of the fifteen elements (including papers, tasting portfolios, exams), I have managed to pass thirteen and just have the wine theory exam and fortified spirits exam to pass at this point before I manage to achieve the Diploma. I may not succeed, but this all goes to show that it is do-able if one works really hard, spends a lot of money on bottles, has huge determination and is prepared for a major time commitment. (The other two non-professionals in the class, by the way, are finding it very very hard going and seem to be unlikely to go the full route -- they both have jobs to contend with. I don'tm fortunately, so I have more time to devote to this.) By the end of the Course, if I do pass, I will feel at least confident enough in my knowledge (not backed up by job experience, unfortunately) to apply for jobs in wine.
It seems to me the way to go is to move onto the Advanced Certificate level first, and see how it goes and how you feel at that point. The leap to the Diploma Course is a huge one from there.