A boat that stays in the water avoids problems like misplaced poppits or uneven supports along with the possible chafe of lifting straps on the topsides. Storing a boat on the hard can lead to hogging, though that's not likely noticeable in a boat like the Bristol 24. If the hull's been kept clean with scrubbings, and the shaft and prop are in ok shape, the concerns are those you've mentioned - saturation, blisters and possible delamination - which would be the same for any boat. The long immersion may call for an especially careful inspection below the waterline, sounding the hull thoroughly and going over it with a moisture meter for good measure. Be aware that it's also possible for
PAINT to blister, and not just gelcoat. The former problem is practically to be expected, especially in a boat that's gone so long between haulouts. I've heard stories about how a scared seller lowered his price by $10k when the buyer pointed out blilsters and said that's what the yard quoted for a bottom strip & barriercoat job. After he'd bought the boat, the buyer took out a putty knife and in two hours had scraped off the blistered
PAINT. You may find some gelcoat blisters as well. If there are just a dozen or so,
epoxy filler can fix them in an hour or two. If there are more than that, get more information and another opinion from your surveyor. Good luck!