I agree that rights/importance are subjective, claiming that all humans should have the same rights seems to be an extremists point of view. I would rather say that responsive communicative humans all have nearly the same rights/importance as far as i can tell, and i would be very self-assured to level of ridiculousness if i did not think so. Non-communicative humans i think i can assign less rights like not thinking they are capable of rearing children, but also to consider them incapable of education to an extend. (indeed there would be no tests)

I would chose the cat above the cow in importance, because cats are clearly more active and communicative. While cows do not exactly have this property. I consider that cats may be more likely to solve problems that get in the way of something they want. Here i used association and analogy, i guess it is very subjective.

Maybe communicativeness should be added to the list that helps find rights/importance. Note that i am very unsure about this, but i can not reasonably give insects the same rights/importance as mammals, i think they have very little importance.(well, most insects) And there is no clear distinction when along the line between insects, mammals, fish what rights/importance is to be given.
I think rights should be part of society, and i can not consider making the rights of humans level and that of animals zero either.