Tourists love all the Royal pomp & circumstance. Changing of the Guard. Royal Jewels in the Tower. Queen Mary’s doll house at Windsor Castle. The chance to be part of the crowd and catch a glimpse, at the Queen’s birthday, Royal weddings, Jubilees, etc.
Someone good at digging can find the £ figure, but Royalty-inspired tourism must be worth billions every year.
Yes it's a big tourist draw and always will be even without the Royal family.