I don't find Betty *ugly*. She's both attractive and unattractive. She's attractive because of her personality but ugly in the sense that she doesn't seem to care at all about her appearance. I mean, even if she buys exclusively from Wal-Mart, they have some nice-looking clothes, and she could wear her hair differently. I don't think she should try to look like her fellow Mode co-workers (although Amanda is smokin') but she could STILL try to do SOMETHING...
And you're right, the show is deeper that it appears to be, the characters all have depth (even the shallow ones, lol) and there's plenty of development. Yet it still thankfully manages to be lighthearted and relaxed viewing.