Based on what I had read about Eddy and Macdonald I was mostly pleasantly surprised by their acting abilities. It was much more clear to me why they were popular than I had realized from the rather dismissive things I had read. But as to the questions. The first clip really tied the idea of sexual attraction to the voice. She dismissed him and was focused on her tenor, and he was smart enough to realize that this was the way to her heart. The interplay which focused mostly on her was well done. We saw him sing with a slight self-mockery which made him much more charming and her reactions as she was reluctantly impressed were believable within the style of the film. And best of all was the twist when we realized he had done this same routine with other women. She was "put in her place." And yet she took it in stride and so we got the feeling that we were only at the beginning of some intriguing one-upmanship between the two. In the second scene Macdonald is mostly on display and she does mock her own style limitations and she becomes MUCH more appealing because she realizes that she truly cannot compete with what the other singer/dancer is doing. A little humiliation and humility HUMANIZES her nicely. Eddy has less to do, but it is clear that he sympathizes with her and is uncomfortable with her embarrassment.
I cannot really address the second question as I have not seen them since very early childhood and I don't remember them well at all.
I was actually surprised that the film was more subtle than I expected -- I am focused on the second scene. The scene seemed conceivable as occurring for the most part -- except possibly the fact that neither the pianist or the customers were as cruel to her for her awkward singing as they would likely have been. I appreciated the fact that they actually at one point completely blocked Macdonald as she was singing for a fairly long time. And the other performer -- at least for me -- came across as a much better seller of the song and APPROPRIATE for the saloon and the style of music. I saw her as being shown as a success not really "a bad girl" and Macdonald as just truly out of place. It seemed more of an artistic judgment of the two performers than a moral one to me!