If you get good pads and ss lines with good rotors (not necessary aftermarket ones), you gain about 15-20% on brake performance. Going to an aftermarket setup is great, but it is expensive. But they have everything setup for your car, so it is pretty much trouble free, just bolt on and take it for a spin. I have seen the Si, Teg, etc brake upgrade. Cheaper upgrade as the aftermarket setup and great result. I would go with these. I would not go with the 4 pot Acura brake as you car's BMC is not setup to run them. If you did the swap, the front will lock way faster then the wheel. This is a huge problem for RWD car. I do not know anything about FWD though...

What have you done to your car so that you want a wilwood upgrade? Put those money elsewhere like suspension setup, tires and they will not only improve your brake performance, but also does a lot other wonders.