I didn't get that at all! I think Juno was taken with Bateman's character because she saw him as a real cool older guy, and he was perhaps a little flattered. As she got to know him, she realized that he was somewhat shallow and immature, and that it was his wife (who at first seemed like a typical yuppie) who really cared about the baby. I think that the whole relationship between Juno and the couple helped Juno to see past first impressions in her perception of people, to "grow up", if you will.
Very good assessment.
And Sonic Youth isn't "just noise."
While the film was in rough cut form I helped arrange a screening for my son and a bunch of his highs school friends. They booed when she said the Sonic Youth line. (They liked the film a lot, but did object to a couple of scenes you can see as deleted scenes on the DVD which imply that Bateman was just an older lech.)
BTW on the DVD, the director (Jason Reitman) points out that as the movie progresses and Bateman gets to know Juno
he begins to dress more and more like her.