it's the rare 80's supra that doesn't need a rebuild. i think it all comes down to storage and/or a really good cover. if the boat was stored indoors all the time, you might be ok. if it's been stored outdoors and gotten rained on at all, expect some water in the foam and that ultimately means rebuild. by the time soft spots start showing in the floor, the stringers have been wrapped all cozy in wet foam for a long time.
even with a good cover, water can still find ways into the foam like the exhaust pipes.
don't ask me about fat sacs and old floors.