Looks wise, there are lots of slight differences between 240 and 260 but to me it wasn't a deciding factor when looking for a car, it was 2 seater vs 2+2. I prefered 2 seater but there are lots of really cool 2+2's out there. I really feel that 2+2 doesn't look massively different, it's just that many people who choose 2+2 do so because they are on a budget, and that budget also applies to the restoration and modification. But those who spend lots of money and time on their 2+2s, and have a good sense of style, get great results.
Similar deal with 280zx. Just look at Simon's 280zx it is one of my favourite zeds on the forum, and it's not a coincidence that it is that way, he has probably spent 5 times more money on it than the average 280zx owner.
I don't think I've answered the question at all, just expressed some of my views, basically I like all the zeds, but I think they all benefit massively from modifications, and you gotta be prepared to put in a bit of cash after buying the car to get it looking nice.