I've been an Adobe Certified Expert for approximately 9 years as of this writing.
If working a 9 to 5 employment position, the certification isn't going to be of any great benefit. In fact, as an employee there's practically zero benefit to any Adobe certification other than merely continued education for self fulfillment. Your employer may be able to advertise your certification to acquire new business, which may indirectly effect you. But that's about as far as the certification will take you in that type of scenario.
If applying for a 9 to 5 position, it may edge you above an otherwise equally qualified competitor if the employer understands the certification. If the employer does not understand the certification, then it may be greatly beneficial when applying for a job. Those that do not understand the certification can often place more value on what it certifies than the actual merits of the tests. For example, Adobe certifications do not verify creativity or ability to design effectively in any way. However, a certification plus a strong portfolio can often edge out those with only a strong portfolio.
As a freelancer or independent contractor, the certification is a huge benefit to acquiring new clients and edging out competitors. The certification gives you instant authority in tools which many savvy clients know are going to be used. I have often gained and retained clients simply due to my certification. Granted, the work still must be up to the anticipated quality. However, the certification is a pseudo-guarantee to clients that there will be no technical issues due to software inexperience. [I recently overheard one of my clients somewhat smugly expressing over the phone: "We work with an Adobe Certified Expert for these art files." My certification gave them a sense of pride in the work. That's intangible and could not be predicted.]
As an instructor it's almost mandatory in my opinion if you are teaching Adobe software. If you want to teach others, the best thing you can do is prove you know your stuff. Certification does just that.
I have never regretted my certification and it has paid for itself over and over and continues to.
The primary thing you should realize is that the test are production oriented. It is not a "design" or "creativity" test. So any situation where there is benefit to your proving you know how to use the application(s) regarding production may be aided by the certification. It's a seal of approval from Adobe stating "We've tested this user and they know our application(s) well." If you have no need or desire to acquire that direct Adobe testimonial, then you may have no need for the certification.
If contemplating certification, I'd suggest just going for it. That is not to imply you can simply wing it. Few (if any) can do that. However, study and take the test for the current version. Often the tests are 6 to 9 months behind application releases. So, the CS6 tests are sill the current test right now even though CC has been released. Testing for CS6 will be easier than testing for CC due to the simple fact that CS6 has less features than CC. The first test is the most difficult test to take. The longer you wait, the more features each application has and the more extensive your knowledge must be to pass. Pass the first test, then every subsequent recertification becomes much easier.
