I think the CFP mark would be worthwhile if one was planning a career in personal finance. It has its pluses and minuses. For the retiree wanting that "retirement alpha", I don't think achieving the designation is worth much.
Personally, I went through the Personal Financial Planning Program with the University of California which is somewhat more rigorous than the just the minimum CFP curriculum (of which is a part of and the main thrust of the Program). I chose to accept certification from the University and not sit for the exam as I would never complete the work experience, pay the annual fees and submit to the FP Boards oversight and control.
I thought it was very worthwhile although fairly expensive. Compared to the cost of retaining an advisor on AUM or some such for the rest of my life, a bargain. I learned a ton and set out to create a sort of "extended family" office which is offered pro bono to many of our relatives and close friends. This has become what I guess you might loosely call a spiritual service as it is given away with nothing expected in return.
It's certainly true that many can learn enough on their own to manage their affairs given the time, interest and willingness to expend the effort. I can say that old saw,"you don't know what you don't know", applies in some cases.