Not to beat a dead horse but as a current owner of both a 370Z and a MazdaSpeed Protege I feel I can add some objective input on this. Check out my album for pics and mod list of my MSP. I realize it's a bit different than a Mazdaspeed 3, but it's very similar in performance, handling and practicality.
--- Performance ---
These types of cars are two different beasts. I like to describe my MSP as a mosquito. INCREDIBLY quick, darty, tossible and fun to drive. Steering feedback makes you feel SOOOOO connected to this car (mazda really has this nailed) and you know exactly where you are in relation to it's limits. It really does "feel" fast, even if you're only going 20mph. And it handles like a dream - you would never believe it's a FWD car.
Fully modified my MSP is as fast on the highway as my stock 370. That however is beyond the reasonable limit of the stock block. I had everything you could do to this car without building the motor and for straight line speed got it as fast as my 370 starts at. Most people blew their motors running this kind of boost. Mine held tight for 5+ years (great tune) then popped when my wastegate actuator broke and I spiked at 20psi
My 370Z on the other hand is best described as a missile. When you want to go, IT GOES! And it cruises through the turns nice and smooth. It definitely out handles my MSP - I can take familiar turns at about 5-10mph faster in my Z but I can't really tell how close to the limit I'm at. I will admit this is my first high powered RWD car so I'm no expert at all & it's quite possible I'm not even close to the limit in these turns.... It's just the car is not as confidence inspiring cause I just don't feel as connected to it. I'm sure with more experience I'll get there. 6 years in the Mazda vs 4 months in the Z can't really give the same level of knowledge.
Thus I'm modifying the suspension on the Z first. Hoping to get it up to par before I start building the power level. And for power potential the Z is gonna have so much in the next 1-3 years the options will be virtually limitless. One of the primary reasons I chose this car over a BMW 335.
In short - my MSP is more fun to drive, but my Z is a better performer in all categories. The MSP is a really "sporty" car, while the Z is really a sports car.
--- Styling ---
Hands down the Z wins. No question. I love my MSP, love how unique it is (I know the orange pearl paint isn't for everyone) but really this point doesn't even need to be discussed. The MSP was a great choice when I was in my mid 20s, and I've seen white ones and love them, but still not even close. The MSP looks good, the Z is just plain sexy!
Both interiors are equal IMO, but I am VERY anal about my cars and my MSP with 100K+ miles on it still looks brand new. Took a coworker out for lunch today and they made that exact comment. Plus the MSP has more custom touches the stock 370 doesn't have yet.
---Practicality---
Mazda wins hands down. If I only had 1 car I don't think I could live with my Z. No practical cargo room, no room for the dog... plus it's just too pretty to carry anything other than my GF in
So yeah, they are both great cars, but each in their own respect. I can agree with a lot of the original poster's points and if I could only have one car it's highly doubtful it would be a Z.
Thus, I feel incredibly lucky to have the privilege of being able to drive both
