I believe that if improvement of life is defined as helping those with cancer or terminal illness, then animals should be tested upon. If one is referring to making their hair smell better or their skin to have a healthy shine...no.
While lower than humans, animals do have certain rights. Think about the commercials on television sponsored by the ASPCA or PETA. They, the animals, do deserve a certain right of life. Outside of that, anything which can help people sustain life and health, animals are the only alternative to unethical human testing.