To boost/improve Yaris, or move on....?

[OTB]

So I'd appreciate your input on this subject, and especially those of you who took the turbo plunge.

My goal: a reliable lightweight car for street transportation that will still give cooper S cars a run for their money in street class time attack. I have a MR-S race car, and don't have intentions of making my street car into a very competitive car. I do, however have a goal of making it road course worthy (preventing oil and fuel starvation, coolant overtemps, brake fade.)

I own: 2007 Yaris USA 3-door with no options, good quality springs, struts/shocks, rear swaybar. I have owned some much "nicer" cars in my day, but I'd have to say this is probably the best street car I've owned. It is a blast to drive, but obviously with a couple limitations. 1) power-I don't need a ton of it, but it doesn't even have enough power to maintain throttle through corners on the track. 2)suspension-front strut tower mounting (or lack thereof) and the rear end "is what it is"

I used to own a turbo cooper s (stock with good suspension) that my buddy and I would both drive in different time attack events, and we did ok. The car was lots of fun, surprisingly strong, and a pain to work on. I unfortunately had a incident with a couple deer and no more cooper.

My question is....to meet my goals above, do I pursue another cooper, or make the yaris a better weapon?

Proposed Yaris plan: Zage turbo kit to produce approx 150hp for some reliability. I think most guys tune for more boost/power than that, but I'm not interested in pushing the limits of tuning and 1nz strength. Better suspension (have custom lower than MI springs made for my tokico reds, or go to damping adjustable coilovers). Limited slip. I bought my Yaris as a salvage (but actually tip top, just a front bumper cover replacement really) for a good price. Zage kit + management (FIC and PnP harness) + tuning + monitoring gauges + lsd+unplanned BS in reality will cost about $4500. Do I have to kiss my front and rear oem brakes goodbye?

Potential other cars: another turbo mini, rsx-s (great setup but hard to find one that some kid hasn't turned into a shitmobile), and I just can't stand the mazdaspeed 3 so don't even go there. If there was an Abarth 500 for sale in the US, I would probably just get one. Turbo cobalt is a real performance car, but heavy....everything is so heavy nowadays. I'm a Colin Chapman kind of guy. All of my other options weigh 300+lbs more than the Yaris.

Back to the question-could the boosted and sorted 1nz Yaris fit my goals (and do it at 1000's less than a used turbo mini)? Would I be able to carefully setup and tune the car, then mostly just perform maintenance, not a never-ending research project?

Thanks for your input!!!