[cmurf]

This is why there's maneuvering speed (VA), or turbulent air penetration speed (VB). It isn't necessary to over design it, you just slow down and, voila, the airfoil will sooner stall than break - and the stall is brief, feels like sluggishness, like a squishy slow stall, not abrupt, and recovery is similar perhaps a bit more abrupt as the airfoil regains lift.

[cameldrv]

Sure, as long as the gust is mostly vertical (usually true), and you're able to maintain below Va. All of the up and down motion in a serious thunderstorm can easily cause you to exceed Va or even Vne. Many aircraft have broken up in flight because of this. Now it could be that in many accidents, it wouldn't have mattered how strong the wing was -- eventually the speed build build up to the point where a big gust would break it, but I'm sure there are many where say an extra 50% strength would have made the difference.

Now that's also not to say that if you're going to add weight to an airplane in the name of safety that the best place to do it is the wing spar, but there is certainly a tradeoff between safety and weight.