For me (a youngster) image comes into it a fair bit.
To sum up Porsche for me, unless you have a 911, they all look quite effeminate. Non 911's are fantastic to drive but you catch your reflection in a shop window and 'steady sailor'. They just don't stand out as much as I'd like for the amount of money you need to spend on one. Wheras the 911 Turbo, really really good to drive, I would like to be seen in one.
I've driven a few Boxter's, 2.7's, S' etc, really good/fun to drive, but ultimately, I wouldn't want to be seen driving it. I've only seen women driving the Cayman and it just doesn't look as 'ard as the 911, no doubt it's good though.
Same with the SLK, driven one, brilliant fun with top down etc, but wouldn't want to be seen in it. Wheras an SL, I'd have one of those.
As above with the Audi TT.
I think the least effeminate cars are the Z4M and the S2000 but they just aren't as hairy chested as the 350z.
But then again, 'you shouldn't car what others think' apparently.
350z = MAN CAR!