Mike I agree with every thing you said. I will say I am a belt and suspenders sort of guy. Neither gel coat or fiberglass is imperious to water intrusion. I know all about barrier coats. But one good bang against a dock during a storm when you are not there, can spider crack the gel coat and start a path way to the core. If I was not a racer, it is one less thing to worry about. A boat is a major investment for most people. I feel a balsa cored hull is an investment risk.
For a weekend cruiser that is left in the water all season long the J28 would not be my boat of choice. But if I want to go fast and could dry sail it I might be looking at the J28.