I definitely think a 350z is destined to be a future classic. I mean, you don't see many of them on the roads as it is, imagine how rare they will be in 20 years time. I suspect now that prices are coming down they will be used and abused by a younger audience, which will inevitably see some being wrecked, or others having high mileages put on them, and modifications will start to come in.
in a few years an early, non modified low mileage car in a desirable colour will be worth a lot. Especially when the big NA engine has completely died and been replaced by small displacement turbo hybrid units. Also rust will start to eat away at most Jap cars on UK shores, so a clean rust free example will be worth a lot.
Its just starting to happen with 300ZXs now, there are a lot of dogs out there at the moment for sale for dirt cheap, but most are not far away from engine failure or rust. soon there will only be cherished low mileage cars left, and then they will start to appreciate as the numbers dwindle even further.