With Plasma packs, I think that's the point, they're not suppose to refill the thirst bar significantly and it's kind of realistic, a Plasma Pack is like a capri-sun pouch a sample, of human blood that's not really going to do much.
The Human body contains about a gallon and a half of plasma, which a vampire could easily drain out of a Human, and fill their thirst bar to the max
perhaps they should have made more variations like a quart of plasma, half gallon.
Case 2, is odd... Vampire power... any powers really, magic too, takes energy, which should be recovered be resting/consuming.
Bottom line, If that energy bar is full Sims shouldn't be tired. All that should happen is whenever sims use their powers it should cost them their energy, thus making them tired.