It would be interesting. I suspect that a 1.8 Miata won't be able to cut it in ITS, but I'd love to see someone give it a good try to find out.
I doubt that it is possible to get a 1.8 car with an average sized driver down to 2200 pounds. Heck, it's hard, if possible, to do it with the 1.6 car! The difference in weight is not that much, but there is some.
The handling will be there and the brakes are good and it will be good on parts and reliability. It comes with 14" wheels, so that also limits the tire choices.
The difference between the 1.6 and the 1.8 in terms of power amounts to about 15, maybe 20hp. Everything else is about the same. I don't know if that would be enough to be competitive in ITS.