The real issue I have with cored hulls is that if throughhulls are not properly installed in them, they can lead to core delamination and core breakdown with little warning. Any delamination in a cored hull is a very serious issue, and generally requires a very costly repair
. I have no problem with properly designed and maintained cored hulls, but most cored hulls are not properly designed, with solid blocks of laminate where the through hulls are located, or properly maintained.
As for hull core materials, while foam has some major benefits, like rot resistance, weight, and such, it is often a poorer choice than end-grain balsa IMHO. End-grain balsa will generally help contain any water intrusion to a fairly localized area to begin with, which foam will not do. It may also be easier to detect water intrusion into a balsa cored hull, rather than a foam cored hull. A foam-cored hull can have much larger areas of delamination, due to the water migrating along the foam/laminate boundary. Foam generally has more adhesion and lamination failure problems than does end-grain balsa as well.
One other thing to consider—the foam core technologies of the 1970s was not very good, especially compared to the foam and core materials available today, so a foam-cored hull from back then is probably at higher risk of having serious lamination failure issues.
I don't know Cooper's reputation, and have never been on a Cooper. if they designed the hull with solid laminate areas for the through hulls, and the previous owners have not mucked it up, by adding through hulls in areas of the hull that are cored, then it very well may be an excellent choice.
However, the boat is almost thirty years old. That is a lot of time for previous owners to make mistakes. The knowledge about the weaknesses and design vulnerabilities of cored hulls was not really well known back in the late 1970s, so I am doubting that the cored hull was designed with features like solid laminate in areas where through hulls were located, as this wasn't a consideration in designing cored hulls that far back.
YMMV. Good luck, but I personally would go with a solid laminate hull on a boat that is of this vintage, as the solid laminate hulls of that era have proven themselves over and over again.