It's refreshing to read everyone's differing opinions. Shows the range of how people here view their cars. While I may not agree with all viewpoints, I don't question that we all chose our Z's for somewhat similar reasons.
I admit to having a certain amount of "emotion" when it comes to S30's, especially 240's. I heartily agree with others regarding the sound of the engine. It's got an underlying, "gritty" mechanical sound, not duplicated in mechanically quiet modern engines. And as stated above, the exhaust music from an inline 6 at higher revs is distinctive. I think the evolution of the L-series engine, (with modification, capable of generating 300+ HP), probably would have exceeded Mr. K's desire for more power...
As I indicated above, the feline, exterior lines of the Z are unmistakable. There are add-ons and modifications that can skew the look of the car in both positive and negative ways. I love to see well done changes that highlight the positive aspects of the Z's design. Interior mods, for me, are more of a form-follows-function thing as far as I'm concerned.
In terms of performance upgrades, better brakes, engine tuning, suspension mods are all worthwile changes, (especially if reversible. to stock). These can be accomplished without any significant change to the look and feel of the car.
Lastly, my view is of the S30 is as a rally, auto-x or road-race car. They were not designed to be dragsters, especially when compared to muscle cars of the era. The Z's at it's best racing through the curves "at-speed".