The first student essay on Jane Eyre had a focused thesis regarding how Jane's dreams functioned as a barometer of her emotions during the course of the story. The point was also made that an attempt was made by Jane to separate her dream life from her waking life, which was also a theme concurrent with the post-colonial prequel to Jane Eyre, WSS (Wide Sargasso Sea).
As far as the difference between these two novels is concerend, the biggest one was the post-colonial setting in which WSS was set. The issue of race was hinted at minimally in Jane Eyre with the description of the mad woman, Bertha, who is Antoinette in WSS. It is this racial issue that is at the heart of the difference between these two main characters in these two novels, respectively.
While Jane can deal with the inequities that have put her down her entire life, she could deal with things on more of a level playing field than Antoinette could. Antoinette was forced to serve a system that, even if she had a good station in life, she wouldn't be content serving the world as run by white men. The post-colonial world was not one in which the Antoinettes of the world were very welcome. She was ostracized both by White and Black people in the Carribbean because of her Creole background---never being able to fit in completely with either group, something which certainly would not have applied to "Plain Jane."