Here's something I've learnt after three years of intense foraging (plants not insects), in spring look for leaves and flowers, summer for fruit and fall and winter you should go beneath the soil for roots. In fall you can also find shrooms, if survival is the deal, go for the big good smelling and good tasting ones, don't bother with small buggers. It's pretty logical really, but sometimes we've been so disconnected from Nature that what should be obvious is often ignored. Following this simple advice you will get a better economy from foraging, because I have deeply experience what you say about burning more calories than what I was receiving and this had greatly to do with not knowing what to look for in different times of the year.
It seems logical enough, however I think that's generally location specific and doesn't take into consideration all environments and conditions around the world; it's reasonably sensible information though.