Not dealing with a Z but just shows that new non performance cars can go really fast and still be stable. In the latest Car and Driver a man was caught doing 147 mph in a Hyndai Sonata, in the picture it looks like hes doing nothing out of the ordinary, just driving down the highway.
I think what drives Z owners to customize their Z isnt the fact that you can put some huge motor in it and make it go fast, you can do that to any car. Its more of the nastalgia and knowing that you have a part in history of Datsun. If you want a fast car that you can drive hard and put away wet get a new car.
To me the reason I have my Z is once I get it on the road, maintaining it and needing to take better car of it then a new car will be the fun. Knowing that I need to take care of it and knowing Ill know every nut and bolt makes it fun to own.