You know I was going to go with grey for mine, but I just didnt like it in person. I seen it on a yellow, just didnt like it better than the black. I also started seeing the suede door inserts turning black after awhile from all the touching run through my mind! In the end I went with black. Hotter in the summer yes, but I don't regret it. I've had it over a month now and I dont think its any harder to keep clean.
And by the way here is an album I remember seeing when I was thinking about the grey. These pictures do make it look pretty good!
Nissan 370Z Forum - SoCal 370Z's Album: Brisk RFI Photographs