Have to change everything in the intake/exhaust to change the car. Larger volume intakes give you the ability to increase air flow in. Simply swapping intakes and exhaust doesnt "open up" air flow restrictions. Changing everything on the exhaust from headers back will increase flow, decreasing backpressure, then allowing quicker response.
The whole half a second thing.....once again that will depend on the driver. Even bone stock your average Joe wont pull the 13.4 that the car is capable of. By no means am I saying you are an average Joe behind the wheel, so please dont take it that way. Best way to find out I guess is to clock your own 1/4 time, swap out all of your air flow parts, run the 1/4 again.
There are more than a few parts out there from different manufacturers that will give you different results as well. Berk for instance has there HFC's that seem to be popular with a few on this site. I personally ordered these from overseas:
http://www.mines-wave.com Just click on the Fairlady tab and scroll down to the straight pipes. Absolutely no restriction with these.