I totally know what you mean about ostensibly 'bitchy' characters having much more to them (if written that way). I can see similarities between all those you mentioned (except Rachel, cause I don't know who she is
).
Believe it or not, I think liking Valerie, for me, had more to do with her sense of humor. Put her with Brandon and Steve (the brief Casa Walsh threesome) and you're likely to get a good scene (relative for the episode, anyway). I know she wasn't always honest in a good way, or a ball-buster, but those were some of her enjoyable strengths as well.