I can't say that I find Connie to be a particularly interesting or funny character. Connie really hasn't evolved much over time; she's still pretty much the same stuck-up mean girl she was at the beginning, only now she occasionally gets some come uppance for her behavior, although it's usually delivered by some other character, be it verbally (Brian) or physically (Peter or Stewie), rather than having revenge exacted by Meg herself, which would be more satisfying to me, since the Meg/Connie interactions are always so terribly one-sided: Connie treats Meg like crap and Meg kisses Connie's ass. And since Connie still routinely treats Meg like the floor on a blind man's urinal, the character has done nothing to edear her to me. However, it's clear that FG's writers feel something for the character, since they keep bringing her back. I'm still not a fan of Connie's, but since FG in general is such a boys' club, it nice to see them pay some attention to one of the female characters, I suppose.
Also, I don't think that the physical similarities between Connie and Jillian were intentional on the part of the animators. That's probably just the way that Seth draws hot blonds.