A fine flier doesn't mean that if you incorporate washout you are going to make the plane worst. Perhaps it will help to be more docile in landings. I have found that the TF P-51 with symmetrical airfoil, 0° incidence is one of the reason many people end it breaking the wing in addition to the poor structural design/techniques used in the Chinese factories for the ARF model due to the fact that the plane needs to lands on the fast side. And you would say oh that TF P-51 flies fine. yes but it lands too fast and not very forgettable, but if this model has non-symmetrical airfoil like a naca2315 or naca2415 and at least 2° washout the model will fly even better and the speed for landing will improve.
Bottom line, if you want even better performance of your Nosen P-51 put some washout and you won't regret about it.