Is a cold air intake worth it for a Mazda MX-5 ND2 …

… with headers, a free-flowing exhaust, Port Water/Meth Injection and a tune?

I'm not sure about the ND, but on this NC we gained a good 22bhp at the hubs with the new inlet manifold and intake. It had the exhaust manifold, exhaust and cams installed previous to coming in for the initial tests

Thank you, that’s significant! But with what inlet manifold and intake?

Thank you again Chris250 for the info, albeit from a 49 year ago dyno run on an NC. Note also that Mazda had made a major upgrade to the engine for the ND MX-5s: a modified CX-3 engine over the NC and earlier versions of the MX-5: where Sake Bomb Garage/MiataSpeed in Fremont California told me that the motor had already been pretty much maxed-out by this time. Of course, that was when they were trying to sell me an Edelbrock Supercharger: $7,000+ just for the kit. With their installation I guess the total would have to be over $10,000. Christian gave me a test ride in their 12 psi boosted car, with its necessary water/meth injection, and it was impressive! But I just wanted a little more grunt with fewer dollars, and wanted to keep the benefit of it being naturally aspirated as well.

Also, I see from HPA’s Introduction to Engine Tuning course, that I’ve just purchased along with their Tuners Starter Package, where Andre had stated that using a high octane fuel like VP’s Racing's with a 120 octane rating can add 50% to 100% more power to even a stock engine! Of course, that’s what Water/Meth Injection can also do as it can raise the octane rating of even 87 octane pump gas to over 118 octane—the power increase coming in both cases from advancing the ignition timing.

Which leads me to my next post: “How To Tune For Water/Meth Injection And Not Blow Up Your Engine!” Note that with Water/Meth Injection I will be able to match, or exceed the power gains of forced induction without the added expense, and not have to walnut shell-blast clean the intake ports every 15,000 miles—the need for which I've eliminated in my naturally aspirated car that otherwise would still need to be cleaned-out every 30,000 miles (topic for another post)!