I think the key is the execution of the technique.. a properly built and engineered cored hull is going to be stiffer, stronger and lighter than solid glass. The problem is knowing if the boat was truly properly built.. this means good lamination techniques and properly isolating any through hull locations with solid material to avoid risk of leakage into any coring.
I tend to agree with the 'no core below the waterline' idea too. I feel that any blistering that might occur is a bigger problem with the relatively thin-skinned cored hull.
Of possible interest to you, td, our Caribbean sailing friends opted for a solid glass hull in light of the elevated temperatures in the tropics and how that might worsen any issues that may arise with time in a cored hull.
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)
1984 Fast/Nicholson 345 "FastForward"