The Niagara 35 is a very strong boat, I would not dimiss it for a cored hull.
In my opinion if a boat is properly built and maintained then a cored hull is much superior to a solid hull. Much lighter, stiffer and drier.
There are only a few places where there is potential for water ingress and they are easy to deal with.
I do not know for sure but I would be very surprised if the spots where the through hulls etc are are solid glass. If not that is pretty easy to fix.