NeoSHNIK

Sure. Here are my observations:
1. Many people who install FI end up selling their car soon. Not sure whats causing it, but may be the following points are the reasons why its happening.
2. Cost and time. Getting it done right takes a lot of money and a lot of time.
3. Reliability loss. Many stock turbos have occasional problems. Aftermarket FI cannot be better... our engine is not designed for FI (although its a really good reliable and strong engine that can take this better than most other NA engines). But still, throughout the life of the vehicle, you will have more problems with the car and unless you can work on the car yourself, it will be in the shop frequently. Note that for a track car reliability is not really a huge issue. You kind of expect occasional problems when tracking a car.
4. Hurts resell value... very few people want to buy a car with a used aftermarket FI turbo... Note that for a track car resell is not an issue.
5. Speed is relative. Ok, you are a whole second faster quartermile... now what? Stock Z is faster than 99% of the cars I see on the street. When FI it will faster than 99.7% of the cars on the street. Was that 0.7% worth it? Besides, even with FI there will be plently of cars that will be faster than you. Note that for a track you are no longer faster than 99% of the cars... so you do want a faster car
6. Traffic. It is not very often when you get to go fast during daily driving. Most of the time you spend in traffic, slowly moving, or driving at a constant speed on the interstate. In these conditions NA car will probably feel smoother or at least the same. And during those rare times when you do get to go fast, even the stock Z will put a smile to your face.

Note how these points are not as relevant if your car is a track or weekend car. Finally, I wanted to say that 370z is already an amazing car the way it comes from the factory. One can have a ton of fun with it on the road and adding FI is not worth the risk and trouble for a daily driver.