I agree somewhat on the 86/BRZ being the answer, but I'll parry your monkey wrench with a screwdriver
I say take the new 86/BRZ but DON'T put any forced induction under the hood, skip the BBK, and take the savings to buy some lighter/wider wheels and some sticky summer tires!
The need for more power is debatable now that the new 2.4L engine has eliminated the infamous torque dip. I recently test drove a ND2 Miata with the new engine and even 180hp in a sub-3K lbs car with a nice fat torque curve is properly quick and a hoot to drive. I imagine the BRZ with 228hp in a similar weight vehicle would be just as fun.
A BBK might be needed for extended track sessions or racing to deal with the heat, but for normal enthusiast use and even autocross, the existing brakes are probably just fine due to the car being so light. Just throw on some better pads.
Lately I'm starting to realize and truly appreciate the beauty of driving a slow car fast vs a fast car slow. I currently own a pretty fast car, but big power = big weight and driving a fast car slow is a real snooze fest. Flogging a lower powered light car is a ton of fun.
The Z car here, Supra, M2, Z4, and maybe the higher trim Cayman/Boxters like GTS and GT4 occupy a strange in-between land that isn't quite a fire-breathing Coupe like a Mustang GT/Camaro SS/M4 but too heavy and powerful to be in the same class as the BRZ/86, Miata, Caymann/Boxter.