That would explain how it has more replies than views :blink:
I like your comparison to hunter-gatherer societies, showing the neccesity of "knowing" what you eat, and their subject to climate changes and/or natural disasters. However, hunter-gatherers have one big difference from our LBT friends: they travel around, and don't remain in one place, usually because they're omnivores and have to follow herds of large game animals. Since the Great Valley is their year-round home, they should learn very quickly what plants you can eat, and what plants to avoid. This makes eating more common sense than hunt-&-peck. Spike has been seen chomping into whatever plant seems to be nearby, and rarely has to travel far to find one that's edible.
But, like you said, this only applies when food is abundant, probably spring and summer. Yes, Mr. Threehorn, in LBT 6 I think, mentioned fall as a time with less food, but I don't recall food supply actually affecting the dinosaurs in that film
(though it might have; I haven't seen that one in a while). He might have been grasping at straws to get the newcomer out of the Valley. And wasn't there a TV episode showing them living in winter like nothing's happened?
Also, movies 5 and 8 both established 'safe zones' that the inhabitants can go to when food supply requires that they leave the Valley. Zone 8 is shown to work even in the middle of winter.
That's not to say their life is a cherries&cream pie, but I don't think starvation is as big a deal as you say.