Airex core is pretty good stuff. It is relativly good at NOT absorbing water (it is not completley water tite however). The same procedures for examining balsa core can be applied to airex core. IE: whacking the snot out of the laminate with a rubber mallet to find delamination. This ia a good job for a competent marine surveyor.
I have not seen heat related softening due to high temps and I have seen a number of vessels return for the south Pacific. This doesnt mean this can't happen. I have seen delamination due to impact stress in airex cored hulls, and rarely (but have seen it) seen water intrusion making the hul spongy.
I have not heard of any major deck problems endemic to the KP 46. This vessel was built at the queen long yard and was a serious upgrade from the origional 44. If I recall correctly the 83 was one of the early 46's built.
If you really are considering the vessel, get someone heavy to walk around on the deck, if you don't notice any springy spots the vessel (other than other obvious problems) would be worth a survey.
The KP 46 sails very well indeed and you should find it a comfortable craft. The joiner work from the queen long yard really sets it apart from the earlier 44 and the streched 44 (Spindrift 46).