I have a 1987 S2 27, which is also cored below the waterline. When I bought the boat back in '08, the survey came out perfectly dry for moisture below the waterline. I think the major problem for our cored boats would be with barrier coat (or not!) and improperly bedded through hulls. My boat does have an Interlux 2000 barrier coat, topped with VC-17, and as far as I can tell, the through hulls were properly installed. Regardless, I'm not sweating it at this point with my boat.
Personally, I think cored hull boats get a bad rap...they are certainly much lighter, and way stiffer. But they DO need to be maintained properly.