Owned one. Might again...
The advantages to a cored hull is that it is stiffer for a given weight, and that it better insulates. Many Freedoms, J Boats, C&Cs, and Hinterhollers have cored hulls. People fear water intrusion into the core. From what I've seen, this happens less with hulls than with decks, because *generally* builders completely encapsulate the core in the hull, builders void the core where they plan any hardware going through, and owners don't add holes to the hull. In contrast, most decks have hundreds of items piercing their core, and -- sure enough -- soft decks are a chronic problem on older boats, typically around handrails, turning blocks, or other hardware that pierces the core. I would buy a cored hull again if the builder had a good reputation for its construction techniques, the construction didn't leave the core exposed at any point, and a survey turned up no signs of water intrusion.