I want light weight but reasonable durability.

This brings to mind a variant on a joke: "Light, strong, cheap- pick any two"...

There are different kinds of durability, in my mind.
1)Abrasion resistance- how does the hull stand up to sliding up on the occasional (barnacle-encrusted) rock? Will I be afraid to pull my boat up the beach (or paddle straight into the beach)?

2)Impact resistance- if my boat is half full of water and gets pounded against a rock, what will happen? Or: If I drop my boat in the driveway, will it crack?

The 'solutions' to these two are probably different. There's a lot of thought given to impact resistance, but most of the abuse I see in boats around here (PNW) is in the first category. That said, a friend did have his WS glass boat crack the hull laminate when it slipped off the roof rack.

For stiffening the deck in front of the cockpit (if necessary) it would probably be lighter to add a thin 'beam' (strip with tapered edges?) and glass it over than to use heavier glass throughout. Lately I've been making glass/CF cockpit coamings and the 'wrapped under' laminations add plenty of stiffness to the deck.