While I think it is a very important step for Emma to believe in fairy tales, I don’t think her belief in magic is enough to break a powerful curse. I think her belief will be very instrumental in her learning how to break the curse though. Based on the episode description of ep. 17 Mad Hatter, a mysterious and dangerous man with a knowledge of the curse (i.e. Franklin/Mad Hatter) is going to kidnap Emma and try to persuade her that fairy tales actually exist in SB. I think this kind of shocking situation will cast some real doubt on her skeptical nature.
"That’s how you know you’ve really got a home. When you leave it, there’s this feeling that you can’t shake. You just miss it." Neal Cassidy