As someone not from the UK, I think the royal family is one of the unique things and while it's an oddity they might as well make the most of it and put on a show for the coronation.
It's a good advert for UK PLC and the streets all hosed down looking nice broadcast worldwide is cheaper compared to running a big ad campaign for the country. The money per head wouldn't stretch to more than a pot noodle.
Charles has said he want's a coronation that's value for money, which seems like the right choice to benefit everyone.
But in these tough times they could announce a plan for the crown estate to boost revenue and how much they pay into the coffers. Maybe open up Buckingham palace way more?
Australia no doubt spent millions on this to promote their country.