As soon as I posted that I knew somebody would mention that. Lets put it in to perspective:
The royal family costs us £41.5m/year. The royal wedding itself is costing $48m. In addition to that the additional public holiday will supposedly cost the country around $10/bn, although I'm not really sure where the site I'm reading gets that figure from.
Regardless, they are all very substantial sums of money. Buckingham Palace only earns around £7m/year in tourism revenue. Even if all of the royal-related tourist attractions pull in more than that per year as a whole, I cannot imagine it is by a substantial amount - Certainly not by enough to justify an utterly undemocratic head of state and an entirely outdated system of privelage.