These days not a massive amount, certainly for the money you pay a main dealer. It used to be a very important part of buying a new Harley with a carb as they all came out of the factory with huge flat spots at the rev ranges where California emissions checks were made. The new fuel injected bikes don't have that problem as they are mapped for each market. Mostly they now just make more noise and another 5-8 bhp.
I'd ride the bike first and then decide if you need it. I'm surprised a CVO needs it
Now if you are going for stage 2 that's a different matter