The understeer is inherent in the car.
My car has no VDC and it still understeers mightily, especially on a wet skid pan.
I get the feeling its just us, though. The car is set up with a wider rear track and front heavy, and making a car nose heavy and providing more grip at the back is hardly going to make it inherently darty in corners.
I get the feeling that you just need to learn the car, and you can dial most of it out. I remember how heavy and unwieldy the 350Z felt when I first took it for a spirited drive, but then I was trying to chuck it around like my Pulsar SSS.
The Z is a car that encourages you to drive properly (or punishes you for not). Once I learned to slow a little more for the corner, trail brake if necessary, and be smoother on my turn-in inputs, and then rely on the copious rear-end grip when I power out from the apex, the car is quite responsive and quick. 1500kg is never nimble, but you can go quite quick.
Of course, if you have VDC then the option of trail braking isn't there for you......
I went up on the Old Pacific Highway last weekend, and I drove with a friend in an S15. His car makes around 170rwkW (so more than mine does) in a 1300kg package. He also has brand new tyres. On the open, sweeping sections up to the Calga Interchange, I'd get away from him. If the straight was the right length, he'd catch me. On turn-in he might make a smidgeon of gap on me. On exit, I'd pull away. Where I can floor the throttle in the meat of third gear and be sitting there begging for more power, he has to feed it in gradually or risk the rear breaking away.
Once we went north of Calga and the road tightens up a lot, however, it was another story. I was fighting the car and trying to keep it from understeering off the road, and he was driving at 6 tenths to avoid running into the back of me. At that point, the extra 200kg becomes telling.