I'm not so sure about this point, but I think people don't want to see a male character who is weak and vulnerable. I don't believe she was just eyecandy, her character also helped to develop many others, like Kim, Janeway and the Doctor. It explored the fact that it doesn't matter where you come from, you can still be accepted by others.
Yes the reactions and relationships the other characters had to her brought out their own personality and contributed to their character arcs. The EMH had the same effect.