This can be explained with a few principle elements of human psychology and social behavior. It's something I might expect. If it was only her attractiveness that was drawing me to the class, I wouldn't bother thinking about it. But I hear she's a good teacher and that her classes are pretty fun. The fact that she's pretty is some very good icing on the cake.
Crap. I really want it but it might not work if actually get my physics class, and if I start working. Scheduling is far easier when you only have to go on campus 2 days a week instead of 4.
haha, the Halo Effect: the tendency to associate more positive traits to beautiful people? Stuff like that? I don't think it's necessarily bad to pick teachers partly on looks unless you are a creeper. LOL
Personally, I'm easily bored/distracted enough in classes, I really don't need a teacher that is going to cause me to pay even less attention to the material. (Yeah, I might be paying attention to her, but that's not quite the same.)
If your goal is to score with the teacher and you are confident of your abilities in doing so, you don't need to join her class at all. There will always be opportunities to fraternize with her outside of class.
Save the money, and study hard. You will meet attractive women all your life, and spending a substantial portion of your budget for a minuscule shot at just one of them is hardly worth it. Save that money. Buy yourself some nice clothes, sign up for yoga or anything that would actually make a difference to your chances of getting laid.