Pack a suitcase full of cash and throw it off a cliff. That’s how fast new Rolls Royces depreciate.
So, no, they don’t retain their value very well at all. Not only in percentage terms, but in the sheer amount of cash lost.
Part of the problem is, most people that can afford a Rolls Royce can afford a brand new one, so there aren’t as many people prepared to pay $200k for a used one as there are that are prepared to pay $300k for a new one.
That’s not to say that there aren’t models that retain their value or even increase over time, but for these, you would have to look at the classic Rolls market.
Something like this would be an exceptional investment: