I would not try to put a value on a being's life because to that being their life is very valuable. Sometimes it's difficult, people put a hierarchy on living beings' lives. But if one gets closer to that particular being we realize that for that being its life is very valuable and no being really likes to die or be harmed.
However, as far as Kamma goes, I think that with most beings that actually give things to human beings, help us in some way, especially the domesticated animals, our harming them will probably give us more unbeneficial Kamma because they've already given us something and provided something for our life.
This goes on to the other questions, "Has every human being the same value?" And, "Is killing the parents worse than another person?"
With this last question, according to the Buddha's teaching, yes it is worse, because our parents gave us human life and took care of us when we were helpless. So it appears that in Kamma if a being has actually given us a lot and we harm them then we are going to get worse Kamma for doing that.
It's very difficult for me to answer these questions because I am not a Buddha, and one of the things the Buddha did say in the scriptures that I recall is that if an ordinary human being tries to figure out Kamma they will go mad, because only a Buddha could understand the complexities of Kamma.
"Is killing an average westerner the same as killing an almost Buddha-like person?" No! To help you understand this more I'll give you a listing of some actions that, according to the scriptures, carry very heavy Kammic consequences. These actions are killing a mother, killing a father, harming a Buddha, or killing an enlightened person. These are very negative Kamma, very long lasting Kamma. Killing a mother is the worst thing, due to all she did for us in order for us to be alive. With killing an enlightened one, the purer the person apparently, the more heavy Kammic consequences you get.
But as far as making a judgment, it may be very difficult for me when it comes to animals and living beings to start put them into a hierarchy or level, although most of us will probably feel worse about killing something bigger than something smaller.
However when we consider that a termite lives thirty years and has big termite mounds, with intricate cities and societies within those cities, it is very difficult to say that they are any less intelligent than something that is bigger, like a mouse or something that doesn't have the ability to build such big things and have these societies. We can't actually take it on the bigness of the animal either. So I will leave that to the Buddha to try to work out, but certainly killing is something we try to avoid as much as possible.