The truth is there are no right answers.
The preservation vs. restoration debate is a good example of this.
On cars
Personally, I don't think a mid-sized car made by BMW is a 'Mini' even if it says 'Cooper' on it, has white stripes on the bonnet and is actually a very good car. If it followed the original design philosophy with modern enhancements I might think differently.
I am happy to accept one of the Brazilian-built Beetles as the 'real thing', certainly more genuine than a modern Volkswagen 'version'.
As for the E-Types. Not only are Jaguar the original manufacturer, the cars are essentially built to the original design. The chassis numbers are a distraction, but no-one is being fooled that these are fifty year old classics, they are new production of an old design and no doubt roundly superior to the originals. But I feel they are E-type jags, just as Tornado is a 'real' A1 loco.
The Rocket is a good example. That in the Science Museum is the 'real' Rocket, albeit much modified from its original condition. The replica is, to my mind, a modern continuation of the original production – a 'Rocket-class' loco, if you will.
Another example is the F1A engine used on the Saturn V rocket. A hugely effective design, it has been resurrected as the F1B using modern manufacturing techniques.
Neil