I suggest you invest in a good steering wheel, pedals & sound system and buy the latest Need For Speed game. 

There is no way to get serious power out of that car without sacrificing reliability. There just isn't. It was designed as a great handling little roadster, not a powerhouse track car.

Save your money. Miata builds always wind up going sideways. UNLESS....you want to swap an LS motor into it. But I'm guessing you don't want to spend that much. 

My suggestion is to leave it alone and get another car.
I wouldn’t bother modifying a Miata.

get a car that’s worth modifying, some can be bought for cheap with relatively low mileage.

— from my personal experience, this is probably not am the best advise:

There are cars you can easily get more power out of, I’ve seen people get over 300+ horsepower out of a manual 5 cylinder Volvo C30 I know a guy who modified his when it was brand new and now at 150,000 miles it’s still solid and as reliable as a stock one.

(I own a Volvo c30 and ive seen many people in car meet ups do cool things with them)

(Note that some parts are hard to get outside of Europe and specifically Sweden 🇸🇪)

some people online claim that you can get 600 horsepower out of the PoleStar edition (and Jay Leno said that that’s something kids in Sweden do) but in that case it does probably significantly affect the reliability.

I would maybe upgrade the suspension for better handling and get some good street tires. That wouldn't give you more power but, it would be a fun reliable option.

There is a lot involved to add a turbo properly to a car.  You just can’t put one on and call it a day.

See below:

https://carkiller.com/scottykilmer/qa/turbo-conversion/#post-56614