Coil on plug has been done but only works on Megasquirt or you can get a reflashed Evo 8 Ecu with a engine harness that enables it.
It definitely is needed if you are thinking of going high hp ie 300+, the stock dizzy system from what i've heard is awful.
The Miata system had one coil pack, and a CAS to control the signal to each cylinder. This increased power, mpg, and spark. If you go C.O.P you gain a good amount of performance with it.
I think you could get it to work if you got a Miata CAS, and then hybridize the Miata ignition harness with the Capri harness.
With the Evo Ecu you have to use the Miata CAS to run it.
I plan on getting a reflashed Evo ecu with it.
The only people I know who use C.O.P is GTX guys, I havent heard of any Capris, or 323 GTs converting to it yet.