Venice is significant to Jane Eyre because Rochester holds a lot of power and knowledge of the world, especially since he's had lots of experience travelling the world. He tells Jane that once they're married, they will travel to "Paris, Rome, and Naples: at Florence, Venice, Vienna."
In a blog post by Jen, she argues that Rochester holds more power over Jane before the incident after Thornfield is set on fire. During Jane and Rochester's early relationship, his stature is very stately, wealthy, and powerful. He is a man of the world, someone who travels and has more experience and knowledge than Jane.
This location illustrates Rochester's higher social class and wealth and perhaps his willingness to bestow this wealth on Jane as he attempts to buy her expensive gifts and an expansive European honeymoon. But Jane isn't pressured by his wealth or stature and affirms that she wouldn't accept such gifts, though we are given her fondness for London.
Mapping this location on COVE reveals how the novel's first-person narrative limits our perception of what we see or don't see of Venice. Although it is only mentioned once in the novel, it's significant to the romance shared between Rochester and Jane because he wanted to share his wealth and worldly experience with her.
Source: power dynamic between Jane and Rochester – The Nineteenth-Century Novel
Picture: mine