This is a great post! So I thought I'd give my opinion for what it's worth (usually very little!)
1. Totally agree! If you've overstretched yourself financially you'll never really enjoy it. You'll forever associate it with the stress of financial hardship. People only look at the cost of buying a car, never of using it how they want to.
2. True again
3. If you're in this situation, spend a few hundred quid on some advanced driving lessons. Not only will you be able to get the most out of the car, you'll be safe and find that you're using WAY less fuel in normal driving conditions. It's not as boring as you might think and you wont be lectured on not breaking the speed limit the whole time.
4. Agree again. If it's not right, get something else. A car is a car. If you change your mind again, it's not like a 350z is hard to find.
Basically, are you imagining something realistic? I've seen this before with people caught up in the romance of a race car on the road...they quickly found out race cars are horrible, loud, uncomfortable, impractical, unreliable things! They weren't prepared to accept that.