My view on boat 'sturdiness':
What's 'tough' enough for one person won't necessarily suit another.
Have you ever noticed that some kids wear out clothes much faster than their siblings? :-)
Do some experiments if you want to satisfy your own curiosity. Put a piece of 1/8" plywood over an open bucket and hit it with a ball peen hammer. Repeat with the same plywood, glassed on (one or) both sides.
BTW, adding 'complete' 4 oz glass coverage to a multi-chine S&G boat won't add much weight vs 9 oz glass tape on the seams. Also, IME, adding a light glass layer doesn't add much weight if you are going to coat the boat with epoxy anyway - the glass acts as a convenient 'thickness gauge'.
What will add weight without strength is making fillets too big, adding more epoxy where it's not needed, etc.. "No point leaving this extra epoxy in the mixing container; I'll put it on the boat!"