First of all, the above insects were almost certainly farmed. Pre-agriculture, I'll admit that one could eat raw meats infested with maggots(assuming, that is, that they liked such fare, I certainly don't) but that's about it.
Acorns aren't too digestible by humans. I believe they were a last-resort "starvation-food" in mediaeval times, but not a staple, otherwise.
One point about eating plants is that if you get most of your calories from plant-food then that requires that you need to spend most of your time eating whereas carnivores are able to take time off, due to the high level of energy from animal foods.
I would like to point out, that for many primates, insects are a preferred food. Generally they are a small, but arguably important part. However, when they are plentiful insects can make up a majority of the diet.
Edit: After a brief google search:
"Insect food is the predominant animal matter resource for primates. Insects are eaten by all extant apes, i.e., chimpanzees (e.g., Lawick-Goodall 1968), orang-utans (Gladikas-Brindamour1), gorillas (Fossey2), gibbons (Chivers 1972, R. L. Tilson3), and the siamang (Chivers 1972), and by most monkeys and prosimians. The amount of insect matter in most primate diets is small, but may expand to more than 90% of the diet when insects are abundant and easily captured. Since palatable and accessible prey species often occur only seasonally (Hamilton et al. 1978, Hausfater 1976), the amount of animal matter in primate diets can change dramatically throughout the year."
http://www.curtbusse.com/pubs/HamiltonBusse1978.html