No idea. I never bothered to become an ACE in any of the Adobe programs though I know some of them almost intimately. Having that badge would have no benefits above and beyond what I'm doing, anyway, which I guess is the whole point - it doesn't guanrantee me a better job or any job for that matter... Well, I'll let the others provide some more useful advise as obviously I'm not an expert on becoming an expert *lol*.
Yes, ask yourself one question, "How will an ACE will help me make money?"
If the answer is anything like "I do not know," then save your money, assuming the test costs, and just get yourself trained.
I have never met an ACE who was better at any Adobe product than anyone else I know.
The best way to study for the ACE exam is to read the Help document. Seriously.
Whether it's worth it to take the exam... I'll leave that question to Mylenium and bogiesan.
Ace certification may be required for some teahing jobs, but it's like a PHD in art history. It won't make you a better artist but it may get you a job in education. The study to get the certification however, will be of great value.
I think Rick's point is important. ACE Certification has little benefit beyond education, but setting achievement of an ACE as a goal is a great way to sharpen up your AE skillset.