No hate here, Nacra makes some great boats! I personally wouldn't consider a Prindle.
The repair is easy enough, and the crossbars come off with 4 bolts each... really couldn't be simpler. Definitely a repair worth disassembling the boat for. Personally, I'd buy a 1987 boat in a heartbeat over a 1978/79... those boats are just at end of life because of delamination issues, in my experience... though I just picked up some '78 hulls which seem solid. Maybe I'll get close to 10 years out of them, like I did my last set.
Spider cracking in gel coat is nothing to be concerned about, most boats have that. My '08 H16 has them all over... it's just a byproduct of the boat flexing over time, no big concern there. Delam in the decks is repairable (did that as well to my '79 boat, and it held up for 5+ years... it would've held up longer, but the sides of the hulls started to delam... in my case because of an unrepaired ding/crack in the side that allowed moisture to get into the foam core... same thing that caused the deck delam, actually... As long as you promptly repair any dings through the outer layer of fiberglass, you shouldn't see too many issues with delam). Decks are common areas for delamination, but that's from the repeated compression from sitting on them. Mine were rock solid after epoxy repairs (drill & fill method), and I'm confident any boat with similar deck delam could be repaired without too much concern.
However, if you haven't noticed, this is a common theme with older H18's... they're approaching end of life due to delam issues, and it's getting to be a chore to keep them in good working order, and the "good ones" are getting harder to find. It's still a great boat well worth buying and sailing, but it's unfortunately nearing 20 years out of production... most are 30-50 years out of production, and fiberglass boats just don't last that long.