Our professional opinion is that no paint, clear coat, etc should be sprayed over newly plated parts such as the brake booster. If the car lives in a nice environment which most of them do, there should not be any issues with plating quality going away. If the parts are sprayed, you will lose some of the rainbow tinting in the gold.
The brake booster on my 1967 Z28 looked as good in 2006 as it did in 1991 when I restored the car.
Jerry