The "Vital Lesser Healing" most definately does not work. It gives nothing instead of the described +2 life to your hero. But if the opposing hero uses it, then it DOES work. One of the sacrifice spells also did nothing at all - can't remember which one it was. Neither does the next level Vital healing spell!

Am I doing something wrong or is it just typical Nival Interactive shoddy quality?

Lesser Healing is a recycling enchantment spell, so after it is cast, it is displayed on enchantments panel, where can be clicked for healing. I guess that next level vital healing is Healing in Etherlords 2, it heals caster up to 50 %, so if you have 50 or more percent of life, it doesn't do anything (in case of Greater Healing, if you are full life or more, it has no effect). I also guess that the sacrifice spell you mention is Martyrdom or Ether Feeding (or Dissolution), they are also recycling enchantment spells, so after they are cast, they go to enchantments panel and there can be cast for effect. And because Lesser Healing, Martyrdom and Ether Feeding (and Dissolution) are recycling enchantments, they can be cast as long as they aren't removed.