I don't know if it was true - or how it was arrived at if it was - but I read some years ago that the late Queen supposedly owned one sixth of the surface of the world. If it was true at all, I presume it would have all gone to Charles.
My personal main beef with the idea of monarchy is that the UK is lauded as a proud democracy, when we actually aren't at all. If the head of state cannot be voted in or out - and even if (heaven forfend) they were assassinated by an extreme detractor, we would still end up with their son or daughter - we are effectively a benevolent dictatorship.
When you realise that, had Charles not had children and if he met his end, we would then have Andrew as king - and we could do nothing whatsoever about it (and we've all seen what happens to peaceful protestors against the monarchy).
I don't buy the idea that they are just a figurehead either: they have a huge amount of influence and sway behind the scenes, which they have used on numerous occasions.
Even if they only ever strictly enacted what the elected government told them to do, they would have the complete freedom NOT to do so at any time. Our democratic 'rights' come purely at their perpetual whim.