And the stock tune might auto-correct any possible air flow gains by pulling timing or closing the throttle to get torque back to stock to what it's calibrated to see, unless you tune.
Spend your money how you want to spend it, IMO.
BTW:
(go to about 9:41 for the numbers, but if you only go from this point, know that these are SAE numbers and Andrew's comparing to stock CB SAE dyno numbers. Additionally - because he was running the Interchiller for both runs, heat soak effects are as eliminated as possible. This is probably, so far as I know, reasonably "scientific" CB test there is. It wasn't same day and same conditions, but SAE corrects for those variables, to my understanding, and that only leaves a few other smaller dyno-details, like tire pressures, strapping, etc.