I hear & see so many people who tell me their car will be a classic one day and are keeping it, yet on inspection, they're not even up-together now, let alone in 5 -10 years time !
If you want to see a return from a Zed in 5-10 years time, I seriously think you need to have, or get hold of one of the less produced models (M Roadster, M Coupe or Alpina), rather than the more mass produced standard models. And, the lower the mileage the better. Plus it needs to be tip-top too.
You'll also need to garage or dry store it and tread the fine line of keeping the miles down, whilst keeping everything on the car ticking over, as sitting doesn't do a car any good in the long run. Every moving part needs to keep moving occasionally, otherwise it just seizes or squeaks !
...Just my opinon !