Cored or NOT cored?????
Good question. I think another thing that should be tossed into the choice decision is whether the choice is relative to a new boat or a used (maybe 10-12 years) boat.
With a new boat that will likely be sold in 3-5 years I''d lean more toward coring in any area where it''s beneficial to what I want from the boat in terms of performance, comfort, quality... If the boat is new(and from a reputable builder) then it should be fine & after it''s sold it''s no longer a concern for me.
With an older boat, from a time when closed cell coring maybe wasn''t used as much as balsa & plywood, my choice with regard to coring would be much more conservative. In that case I''d go with an all glass hull and accept (with a rigorous survey) that the deck will be cored with balsa or plywood as (I think) most were.
As always, Jeff''s comments regarding how the boat was built are right on, but on an older boat, even though it was built perfectly, you can never rule out the previous owner punching unsealed holes or not maintaining the ones that existed originally.