I'd suggest corksport camber plates if the Mazdaspeed ones don't come with plates.
Get much stiffer springs, but don't lower the ride height more than an inch. Maybe even not that much. If you DD the thing go for the highest rate springs you can stomach, maybe start around 400 lb/in.
More rear sway bar, unless you really go balls out with spring rates. You should do springs before selecting a bar, but I'm guessing the tripoint bar will be ideal.
The other suggestions are dead on. Priority one is to get on some real autocross rubber. I'm on Z2s, but rivals, and re-11a are also great. Rs3 are great in high heat but slightly outdated relative to the newer generation. Really though, any real autocross tire will be a big step up from the potenzas.
I agree with the sri suggestion too, and I'd add that if you want to do a full effort STF build, you can also do headers, exhaust, and get a tune.