You hit the major nails on the head. Cost - much better Miata. Speed - much better ITS. Level of competition - probably the same, depending on where you are in the country. The Spec nature of the Miata means that you will be much more likely to be head-to-head with someone in Spec Miata, but there is no arguing with the fun of going FAST!!! Also depends on the types of tracks you run. If you are a Road America / Mid Ohio / Brainerd kind of guy - ITS is loads more fun. If your local tracks are Blackhawk / Grattan, then the Miata will be remarkably quick.
I am not a mechanic type guy, so the limited mods in Miata actually is a plus for me. More time on track knowing I am losing because of driving as opposed to less time on track (always working on the car), and never really knowing if I am losing because of the car or the driver! In any case, I envy your choices as I have been on a budget-derived hiatus from racing for several years now. :-(
Good Luck!
