Most of the boats we are talking about were built in the eighties or nineties, or even earlier in some cases- like mine. I think the balsa cored decks have held up surprisingly well- most core failures are not the fault of Hatteras' construction but the fault of subsequent custodians of the boats who drilled into the deck and didn't diligently waterproof the areas they'd drilled into. I have so far had more problems with the aft bulkhead- there are a couple of bad areas again in it. Really this should be replaced with a Coosa bulkhead but I am not going to take the boat apart at the beginning of the season, dammit.
Wet core CAN be dried out and treated. Rotten core has to come out. These are treatable issues if they can be quantified and should not kill the sale of a boat that is otherwise suitable. These are all used boats- none are perfect.
And regarding new boats- one of the sainted Pascoe's big issues ( and fairly so) has been the balsa core problems on Sea Rays, I think it is, where it seems pretty clear (at least in my opinion) that Sea Ray has had not only a construction problem on some of their boats which allowed the balsa core to rot, but also a problem in helping out the owners of said boats and stepping up to the plate and fixing the boats or replacing them. That said, I have not checked in on the issue in a while. But as the man said, it's not at all difficult to have a structural core problem on a brand new boat. The very fact that Hatteras yachts built in the seventies are around in numbers to get bought, sold, surveyed, and discussed at length ought to tell you something. For every boat with a balsa-cored deck that has a problem, there are literally thousands out there with no trouble at all.