Depends on your definition of 'improve'. You could end up with a car that's incredibly skittish and crashy and noisy, which isn't going to improve the car at all IMHO. The Zed was designed and engineered with the weight very much in mind, and the final tuning tweaks to the suspension, NVH and steering would've taken all this into account, so when you start altering things you run the very real risk of making those £M's spent by the finest minds at Nissan a waste.
Sure, most of us do that anyway by changing the brakes, swapping the suspension to aftermarket stuff that's stiffer, running larger ARBS etc, but none of that really removes a serious amount of weight. Once you start taking 100's of kilograms out of the car, you might find the end result isn't quite as good as you hoped for. Half of the Zed's charm is that it is such a lardy lump but one that can also be hustled and thrown around big-hairy-chest style into some outrageous slides, which would be lost if it ended up the same weight as an Elise. Different strokes for different folks and all that, but I just wanted to make the point that losing huge amounts of weight won't always make for a better road car.