Possibly wasn’t clear, but my answer was ‘I’m not suggesting that all people or many people would stop visiting Britain if we dissolve the monarchy. I don’t think anyone could really say what the impact would be. I dare say that SOME people, especially certain types of American tourists, may reconsider visiting Britain.’
As you say you can't quantify it. You maintain it may fall, I say it could increase! Imagine if there was no royal family, visits to Buckingham Palace could go through the roof as visitors could explore the place the same way they can explore the Palace of Versailles.
And after all, very very very few tourists actually see a member of the royal family. Blimey, I've lived here for 62 years and I've never so much caught a glimpse of a royal, not even a shit one like Andrew. And despite the fact I'm a staunch republican I've been to places like Hampton Court and the Tower of London and really enjoyed them.