A brand consultancy has calculated the economic benefits.

Brand Finance plc

Now you may say that they are doing this to promote themselves, but that would backfire if they were not using accepted methods for determining brand value and other intangibles.

My paper today reported that Meghan Markle is expected to give a £150m boost to the British fashion industry due to women buying copies of her clothes.

Anecdotally, there are usually people gathered outside Buckingham Palace. I once saw the President of France emerge in a car from the Elysee Palace and no one, locals or visitors, paid very much attention.