Mathematical thinking and problem solving are skills that need to be honed and kept up to date. You do that by learning new methods and tricks constantly. There are disciplines that require similar skills and have a positive cross-over to other skills. Computer science theory is very obvious application. Cryptography is another. The "tricks" in CS or crypto are not taught in school for everyone, yet having the background in math will undoubtably help getting into CS and crypto.
What I wish that mathematics education would get through to students is a better understanding on how mathematical methods are used in a lot of domains. I see too much of a divide between "math guys" and "non-math guys", with the latter group sometimes getting quite anti-intellectual when it comes to math (even if they seem smart otherwise). Even the author of this article has a very dismissive tone, if we just teach people how to apply 8th grade math and Excel, who will be the guys developing Excel and other tools?
Even if math education is learning new methods and tricks, they are not the skill that should be learned. It's the methodology of what it takes to master a new method - learning how to learn.
Just to give a counter point: I regularly use math skills, advanced calculus, arcane series formulations and spherical and hyperbolic trigonometry. A lot of these methods were not taught to me in formal education, but my education gave me the tools to tackle these advanced subjects on my own by reading text books and old research papers.