I think that at least in regard to culture, works of fiction are likely to be a more effective tour guides of what an era was like than nonfiction accounts of that culture.

At any rate, regardless of which you use as your tour guide (or even both), your picture will necessarily be incomplete. Hell, the people who actually live through an era don't even have a complete picture. That's just the nature of life.

Fiction can tell you about what and how people were thinking.

The concept of primary source is orthogonal to fact/fiction.