Soft up front. You want the front of the car to lift and transfer as much weight possibly to the rear wheels. The problem with Z's is that they are very nose heavy and theres hardly any weight past the rear wheels.
The single best mod you can do for traction is a good set of tires. Get some nice fat street radials on a 17x9 wheel. You could fit a nice 285/50/17 BF Goodrich or M/T street radial on those.
As far as suspension stuff, try this;
http://www.powertrix.com/agora...nsion
Go down to where it says "Rear Competition Suspension KIT - Z32 TT - Powertrix". Buy that. Then buy the "Rear Differential Carrier Bushings", and the "Subframe Spacers - Specialty-Z". Go to an alignment shop and get your rear camber and toe set to 0. I'd also recommend a rear strut bar and stiffer sway bar to keep the rear wheels planted and eliminate flex in the rear.
Another thing you can do is relocate your battery to the trunk. This will shift a good 30 pounds from the front to the rear of the car. Put it in the passenger side corner of the trunk, under the tail light.