Naturally aspirated and down pipe??? Think you're mixing up terminology. Anyway, there are a couple true duals out there for the V6, including ark. None for the 4 cylinder- naturally.
I'll answer this: Are the brembos worth it? Yes. Very Yes. I auto-x my car and never experience brake fade. Even when a friend and I raced together and were having to swap drivers every 10 minutes or so, the brakes felt as strong on the last run as the first. He complained the pads don't have much bite, but I love the fact the brakes can be very well modulated as a daily driver.
The suspension is great, and you're forgetting one BIG item that the track has compared to the base. Limited slip differential. I don't think you're going to piece together a set of wheels and tires, brakes, springs, struts, swaybars, strut bar, and limited slip differential that work as well together as these do for the price of adding these to the car by going track/r-spec.
And EVERY car loses torque as you go up in RPM. Torque is made at lower RPM's and horsepower is made at higher RPM's. Because horsepower is calculated at an inverse proportion to torque. It can't exist both ways.
If you can't afford the V6 track, and were looking at the base, how are you affording this prototype twin turbo kit? If you were to grab a 2.0 track you could match the engine performance of the V6 for less than going to a V6 track. Alot of people on here say buy the V6 if you're content with the engine power and don't plan to mod much. A big reason being aftermarket support, the 2.0 is considered the "tuner engine" and is getting almost all the attention. It can also handle between 400 and 500hp on stock internals (yay evo motor!)
I would drive some of the twisty roads that are behind the dealership, get a feel for the handling there. The V6 is slightly heavier than the 4, and some say the suspension was balanced for the 4, and they did not adjust for the V6. This plus our altitude was a huge contributor to my turbo decision. I wanted a dicey auto-x car that could actually breathe.
The other thing to look at with V6 power adders is you have to get into the motor far sooner than the 4 cylinder, and bye bye any chance of warranty claims then. Bolt ons would be full exhaust and headers, intake, and reflash/piggy back ECU. Next would be going into the motor, modifying compression, cams, boring it out, etc... Not sure how strong the internals are, but if you wanted to add boost, it's a question again of what the stock compression ratios are. With the turbo bolt ons are intake, exhaust, downpipe, bigger turbo, injectors, intercooler, intercooler piping, reflash/piggyback. Bolt on : Bolt on, I think you make more power turbo route (not by much, maybe 30-40hp) but you are lighter and out about the same amount of money when it's all added up.
Oh speaking of power dropping off. I test drove the car and never took it above 5k RPM's, and only did that twice. I was super impressed with power delivery, but as it turns out, the turbo's lose power starting around 5500 rpm. A reflash can take car of this, and I believe hyundai detuned power out of both motors to encourage early shifting for less wear on their warranty'ed motors.
Anyway, like I said your decision, but I would look at your end goals and determine which platform will satisfy you immediately, and which one will make you want to mod it the first week because it doesn't feel right.