I'm pleased to see that Mr. Olivaw is a fellow "onomaniac." I bug the US Census and genealogyroadtrip.com pretty regularly for names data.
I'm going to go out on a limb here. The name Rachel comes from the Bible, in which the character of Rachel is specifically described as a very beautiful woman. A man who names his daughter Rachel (and puts any thought into that choice) probably values beauty and probably sought out feminine charms in his wife, her mother. With any luck, genetics keeps or even enhances the characteristics from the mother.
Of course, this is not very reliable. I don't know many hot Helens, even if Helen is supposed to be hot because of that whole Troy story. (Then again, the Helen story specifies the face, whereas the Rachel story leaves the entire body as fair game.) Meanwhile there are hot Jessicas -- Alba, Biel, Simpson -- inspired by, what? Lady Jessica from the novel "Dune"? And the original Scarlett O'Hara is supposed to be a peculiar beauty, not at all any obvious glamor queen, so Scarlett Johansson clearly raised the bar.
But few things are more depressing than a rather glum female with a hot name. It's as if the couple thought "We know we're not much, but maybe the name alone will compensate for us." Not always.