The Miata's small brakes are better than you think because the car is so light. For track use you almost never need a big brake kit first, you need pads, high-temp fluid, and cooling. Fix those before spending on calipers.
Brake fade on a Miata is almost always a heat problem in the pads and fluid, not a lack of caliper. Address heat and the stock brakes hold up remarkably well.
- Pads first. A proper track compound (Hawk, Carbotech, EBC, etc.) is the single biggest upgrade. Street pads glaze and fade fast; track pads keep biting at temperature. Keep a street set for the drive home.
- High-temp fluid, fresh and bled. Fluid boiling gives you a long pedal. Run a high-dry-boiling-point fluid (ATE, Motul RBF, Wilwood 570) and bleed it regularly. This is cheap insurance.
- Stainless lines firm up pedal feel and are a nice-to-have once pads and fluid are sorted.
- Ducting feeds cool air to the fronts and is the real fix for repeat-lap fade on a hard-driven car. Simple front brake ducts do a lot.
When a big brake kit actually makes sense:
- Heavier/higher-power cars (V8 or boosted, heavier ND) or long, brake-hungry tracks where you want more thermal mass and bigger pads. Wilwood front kits are the popular choice, valued for thick pads and heat capacity.
- Pad availability/consistency at extended track use, where a bigger caliper's larger pad simply lasts longer.
Don't buy the shiny kit first. The community order is pads, fluid, lines, ducts, and only then calipers if you still need them. A stock-caliper Miata on good pads, good fluid, and ducts will out-brake a big-kit car running street pads and old fluid every single session.