Can I ask what makes you think your car is an original Z? Does it have the original paint?
The reason I ask is I am in a similar situation. My car has never been restored, but it is missing the original drive train. I go back and forth on this same question. My car will never be worth the same as a 100% factory original car, but at the same time I don't want the car to lose any more of its its factory identity. I am leaning toward the certification for this reason. I can take pictures, but the 3rd party credibility of Jerry might be better when I try to sell it. Will it add to the value? I don't know, but it won't hurt it. I'd be interested in knowing your thoughts.