While the plot of the DVC is fiction, there is a fair amount of history in it as well. Opus Dei, the Knights Templar, Leonardo Da Vinci, the churches mentioned and The Louvre all exist - the fiction of the book is in the conjecture of how all of these people, places and organizations might be tied together.
Where the DVC might strike some interest is just where Scully mentioned - in bringing up the fact that the NT is a compilation of books that was not codified until hundreds of years after Jesus' life (if in fact there is such a historical character). Just like Brown wrote, there was a struggle by many, many factions claiming to be Christians as to what exactly constituted Christian teaching.
Elaine Pagels' The Gnostic Gospels is an excellent, popular scholarly look into this. There were groups claiming all sorts of teachings, especially the idea of a personal relationship with god that made unnecessary connections with churches or congregations, teaching overseen by elders and deacons, and so on. I enjoyed, as I remember it without looking again at the book, that the gnostics claimed a direct knowledge of god that was experential and not involving a lot of dogma and theology. Of course the men in power didn't like this, so they wanted to disfellowship these heretics. The gnostics' response was that these men lacked their special knowledge of god, were as such not true spiritual men, were completely devoid of authority among believers and therefore were to be ignored!
Even one of the chapters in the old All Scripture Inspired book talked about the development of the Bible canon, and how some books we now accept were left off many of the early Bible book catalogs, and some we reject, or have never seen, were accepted. That shocked me a bit when I first read that as a teenager.
Christianity developed in a messy, slipshod way, and was an extensive power struggle. The DVC presents that pretty well.
S4