I dont think that airlines ever base their acft acquisitions based on how the acft looks. I mean, PUHLEEZE!
Its the economics that makes or breaks a plane. Though I am a fan of the "the bus" as someone put it, i must admit that the 737NG family does make terrific sense.
If you ask me, i dont think they should have discontinued the 737-400 though. I mean it was the best bet to compete against the A320.