oh, I have LOTS of experience with soft spots... Namely, what happens when you DON"T heed the warnings and take your boat out in strong winds... Needless to say, maybe I shouldn't have named her the S.S. Calamity as a joke...
About 1' in front of the front pylon you should be able to "thump" the hull with your fist like a hammer, and it make a thunk sound... If it makes a thup sound, its delaminated... It should sound hollow and rebound your hand. A soft spot may sound like crinkly crackily slightly breaking sound as you push on it gently... GENTLY>>> Don't give it soft spots if it don't have 'em...

But the hulls SHOULD be able to support quite a bit of your weight with out making any noise and without giving. 78-83 I hear are the worst years. I had a '79 that was completely shot, but I didn't listen and almost killed someone when the hull collapsed and dismasted.
True brand new hulls will thunk a little louder, but you'll know a soft spot when you test one. Put weight on them with your arms and shoulders.... You'll know...