Polyurethane bushings definitely help- they really help to renew your chassis by stiffening up all your pivot points. I'm sure that your stock rubber bushings are pretty tired by now.
As for everything else- how much money do you have to spend? I'm a believer that the suspension setup is every bit as important (if not more) than the drivetrain on a car, so do your research. This is what I have and it works well:
Tein FLEX coilovers: 9kg/mm front, 6kg/mm rear (spring rates)
Eibach sway bars: 26mm front, 17mm rear
Neuspeed upper front strut brace
Energy Suspension bushings all around
JimFab traction bars
The handling on my sedan is very neutral, and behavior at the limit can either go towards understeer or oversteer depending on what I do with the gas pedal. It's pretty nice. I'm still looking to maybe get a thicker rear sway bar, more braces (damn lower fronts won't clear the 2.5" collector on the header) and a back half cage.
As for the G-Tech, who knows. Lots of people say that it's pretty good, but I've never used one- and I'm skeptical of a device that claims to measure quarter mile times and estimate power without ever reading vehicle or engine speed directly. I have an Apex'i RSM (Rev Speed Meter) with the optional G sensor. It wires directly into the ECU harness to read both engine and vehicle speed, so it can make real estimates about power and acceleration- it even compensates for wheelspin since it knows when it's happening. The G sensor is pretty responsive, and you can calibrate it to zero when your car is on a perfectly level surface.
On my setup, the highest lateral acceleration numbers I've seen while mildly pushing the car are 0.85G sustained through a tight turn and 0.6G through a sweeper (both around 50mph). Keep in mind that it's pretty hard to look at the meter while I'm trying to concentrate about not going off the edge of a cliff... I don't know what other numbers I've spiked up to. I need to get to a skidpad and try it out. Hopefully I can get close to 1.0G on the circle.
Just for kicks, I made a braking run from 70-10 and pulled off 0.88G of braking force. I know I could have gone higher too- my rotors aren't in such great shape, and I wasn't quite at impending lockup on the front tires.
Hope that helps some.