The strut setup on these cars is ok, but there's a reason they aren't competitive anymore. No camber gain in roll and the nightmare front hubs (hello, scrub radius called...) are challenges that can't be solved with this arrangement.
The Apex Engineering is in my opinion the kit to get. It lets you lower the car and raise the inner arm pickup point to correct your roll center. I've drilled out my stock sub-frame, and that mod combined with the outboard roll center adjuster blocks make for a wizard handling car.
You MIGHT be able to graft in a Miata front subframe, but you'll undoubtedly run into some hilarious issues with this. I say go for it, particularly if you've already exhausted the adjustments in the stock configuration! And post photos if you do.