While they head up various charities and 'good work' as such, their value to the UK is really now only in tourism. People like travelling to the UK to see some of its history given that it is still 'current', so there are palaces to see, ceremonial stuff like changing of the guards. If we didn't have that, it would be one less reason to even travel to Britain I guess, and tourism is a large part of our GDP (over £130 billion). Reasons are, I imagine, diminishing...
When the Queen was alive, there was a very subtle soft power over Parliament because some Prime Ministers absolutely did not want to sit in front of her during their weekly audiences describing what a shambles they were making of the job and how they were failing people. I might be wrong, but I don't feel Charles has that same presence, so that has diminished too.
Anything I value now, I download at best possible resolution then keep on a mammoth 16Tb drive, streamed through Plex. And I'm glad because, over the years, so much great TV especially has been lost forever (not even available on DVD). Because hard drives aren't infallible, I also back it all up to iDrive.