Given my recent experience looking at several S2 7.9... smack the deck of the S2 around chainplates and mast step with a small wrench, work your way out/around the area, listen to the sound... if it sounds hollow RUN SCREAMING... if it makes a thud there might be hope.... if its solid, its probably worth its weight in gold.
I know of which 2 boats you speak but have not sailed on either, so I can't say if the S2 7.0 is built like the 7.9... I suppose all cored boats have these issues at some point... the Capri 25 had me spoiled to not have to deal with that.