Looking for advice on which direction to go in for a track car

You will miss the refinement; both on track and on the way home.

Caymans are quiet inside and ride nice. At the end of the day most folks are tired and having something plush to drive home in is nice. 

A Cayman has an inch wider track width and 6" longer wheelbase than a Miata. The Cayman feels way more planted because of it.

If you want to be truly fast in a Miata you need to be comfortable with oversteer. Note you don't have to drive them this way to have fun but in your case I think you will just end up where you are with the Cayman. You will start fretting about not getting the most out of the car.

Here is another thought; take the Cayman to an autocross so you can probe the limits in a low risk environment.

I have one other question. How far on the limit do you really want to drive?

Here is a video from several years ago:

I am in the red Datsun coupe just ahead of the camera car. Forget the wheel to wheel part and look at what the car is doing.

This is the absolute ragged edge. Do you really want to drive any car this way? 

How close to this do you want to go?

https://youtu.be/FsApTh6m2Xw?si=x61kBQOsdAxRAPw7

Welcome to the Track Car Chasm.  Population: you (and everyone else who stays in the hobby long enough).  In the experience of myself and many others, there isn't much in between "mildly prepared street car" and "fully prepared track-only car" that's worth doing.  If you can accept this, then the exercise is really about being very clear on your long-term goals and budget.

I think you've articulated the challenges of street cars for drivers that want to continue to improve their skills.  Risk to the vehicle and operating expenses (including track day insurance which basically doubles the cost of a track day) are inherent disadvantages.  Taking a nice street car on the track will always limit your progress as a driver due to lack of seat time (money) and inability to push the limits (risk).  Track mods to a street car are basically like lighting stacks of money on fire for resale purposes.

Track-only cars have their own set of disadvantages... mainly that you need a tow vehicle, trailer, and storage location.  If you can get past that, there are a bunch of advantages.  Many good track cars can be had for a fraction of what a street car is worth.  If you buy one with a racing logbook in a respected series, you can almost always sell the car for close to what you paid for it.  The common track cars are well supported with performance parts and know-how.  Full safety equipment with buckets, cage, HANS and harness is far safer for advanced drivers.  And common race cars like SM or SRF give you an objective yardstick on your driving performance because lap data from experienced racers is available at every track in the U.S. This makes coaching much more effective.

If you really plan to do 2-3 track days a month for an extended period, track-only cars are going to start looking like the more obvious choice.

I owned a 981 Cayman... it was nice on the track but I sold it because I was killing it.  I also owned an ND Miata.  Just as fun if not more, only slower.  I now own a Radical SR1, which is similarly priced to the Cayman.  For my needs it crushes the Cayman in every category.  Fast, fun, predictable, safe, reliable, etc.

How close to this do you want to go?

A bit closer than I am now? :) I posted a video of one of my wet sessions at PIR on a forum, one of the comments was "If you tried really hard, maybe you could go slower" :) And then scolded me for missing a great opportunity to explore grip limits at lower speeds. Which was very valid feedback.

Thanks a lot for the amazing feedback. The key take-away for me is that pushing myself more doesn't have to mean significantly increasing risk. I can pick specific corners at each track where I can explore this. And also autocross, something I hadn't thought about from this perspective. And then when I'm really feeling like I need to take it to the next level, I should look at a dedicated track car, not another street car with track mods. 

In reply to ZiggMeister :

In January I did a SCCA time trial and the track was super wet. Because it seldom rains in Vegas it was super slick.

My stiffly sprung car on Hoosier tires had almost no traction. Loads of people came past.......and then went off the road. Of the 25 cars in my group I was one of 3 cars that didn't spin or go off the road.

Yes the rain can be a learning opportunity and it can also be a hard lesson.