I think you need to step back and more clearly ask your questions
Harshness and noise are very subjective.
I am in the camp of the OEM exhaust sound is under tuned: many ways to fix this (I went with a NISMO, which still is a bit understated but a step up). Example: The OEM G37 exhaust is more aggressive then a Z, which is unacceptable
The second part of the engine sound equation is intake, which IMHO is actually quite good in the Z. Its got a good growl without sounding obnoxious.
Coming from the honda world, then into a Miata (I known them inside and out, having driven NA/NB/NC, and owned a FM II NA6 for 12 years) the NA/NB engines were very harsh compared to a Honda engine...but I learned to live with it just fine. I think that quite a few Z owners are in that camp too.
Mazda spent a lot of R&D on the exhaust tune of the Miata, its one of the defining characteristics of the car.
NVH often is a function of chassis and tires. We own a 2010 roadster (which basically replaced my FM II Miata), and I can tell you road noise in the car is because of those enormous tires, but compared to the NA6 miata, the Z is quieter in every respect. Even with those big donuts, road noise is subdued compared to running 15" Kumho V700's on my old Integra...tires matter
The Z has a much stronger chassis with almost no bump shake, quieter top (layered cloth vs. 1 piece vinyl), and less wind noise at speed.
Subjective still, but if you actually measured things with a sound meter I would bet you will show lower readings. If you are not happy with how the Z feels then don't compromise on such a thing: continue to drive a MX5 or whatever ride makes you smile the most.
When we went to replace the miata, we had a list of must haves...we didn't sway from that list. Somehow, we ended up on the Z. Is it perfect? Hell no. But for the money, we thought it was a fantastic package for what we were looking for.
My top 3 wishes would be:
A real exhaust note from the factory
smooth out the valve train above 5000
Can a brother get a clutch that doesn't clunk at low speed please
- b