I've never had the same model twice, I like to try different things, not just an evolution of the same model. I like to try different marques too, I've had 1 x Toyota, 1 x MG, 3 x Fords, 1 x Renault, 1 x Peugeot, 2 x Fiats, 1 x BMW and 1 x Alfa Romeo.
Variety is the spice of life and all that, I'd never trade in one resale silver repmobile for a slightly younger resale silver repmobile, but then for me cars are a bit of a hobby and my commute to work is a chance to enjoy myself rather than just have a commute to work.
Edit: I'm guessing by your avatar we're not talking about resale silver repmobiles?