I can give you a different perspective from the UK.
First off, I agree with most of your points but for me it starts and finishes at the styling. I don't dislike the styling of the 350Z but it's a bit of a boiled sweet design and lacks the classicism of the 911, for example, which it plainly tries to emulate. The doorhandles are quite disgusting, another no-no for me. Plus here in the UK, we have the opposite problem - the Mustang is a glamour model with peole following you to photograph it and 350Zs are a dime a dozen.
The two cars are about even on power especialy with the upgraded 2008 engine on the 350Z. Stock, the 350Z handles far better but the Mustang is not only it's equal, it's better if you put on Roush suspension and some decent tyres. In fact, here in the UK in a driver's car test, the Roush Mustang pushed the 350Z into 3rd place.
The driving position you are right about but then you can get that in an LS1 Camaro.
For me, I respect the 350Z and would never under-estimate it but when it comes to modding the Mustang has it beaten hollow in looks and performance. The difficulty you have in the US is that familiarity breeds contempt and you should not be blind to the incredibly good styling that Ford have produced. It's not perfect but like the 911, the 60s Mustang design has always been a classic and had Ford pursued an evolution rather than a retro look, I'm sure it would be moulded more along smoother 350Z lines (itself re-inventing rather than retro-mimicikng the 240Z/Fairlady).
For many, the quest to drive something "different" will always be the deciding factor. In this case, neither car will leave you feeling short-changed but the choice may depend on which side of the Atlantic you're sitting. I would check the Nissan price though as here in the UK, the options can soon turn the car into Boxster competition - it's a lot extra for the orange paint and upgrades.
I also prefer a V8 to a V6 - end of. Also being a 2 seater, I'd be looking at used Corvettes as competition for the Zee.