Haha, Chips and gravy.
Having lived most of my life outside the UK I think I have a grasp on why people visit, they go to see the historic pubs in London, the castles in Wales and Scotland, Shakespeare's stuff in Stratford, the lake district, Edinburgh, Scottish Highlands, Buck Palace, Windsor, Baker st, Abbey Rd, York Minster, British Museum, Bath, Wells Cathedral. All these historic things and more. Not to see members of the RF.
Im still interested where this 500 million a year figure comes from, I dont believe it, most of the tourists would still come for the above, and I wouldnt mind betting that the RF as a whole entity costs more than that.