Cell

I went with the Nismo because I just love the body much more than the regular Z and on top of that the rims. Nismo rims > sport package rims in my opinion.

1. If you are refering to the spring spacers then yes the ride quality dramatically changed. It is much more softer without the spacers. It is still stiffer than the base but has a more sporty feel.
2. I believe it is only .4 inch lower than the regular Zs. Not much difference. The only problem is the front bumper sticking out too much which gives you problems going up and down ramps. Most speed bumps I do not have an issue with.
3. The two car performance wise, there isn't really much. The feel of both cars are a bit different though. When I test drove the base Z it is softer on the road.