Canon: Closed or Not?

Since the time of the Reformation (ca. 1546), when Protestants and Catholics officially chose a different number of books for the Old Testament, the canon has been considered closed. Yet, as technology has advanced and as more and more ancient manuscripts have been discovered, the question of the canon creeps up again. Many of these ancient documnets, like the Dead Sea Scrolls, were written either shortly before or at the same time as the New Testament writings. Yet because they offer different perspectives on issues such as Jesus' divinity, earthly faithfulness, and life after death, they are considered useful, but not "holy." Given that the centuries since the Reformation have produced as many questions as certainties about the Bible, what do you think can be gained (or lost) by studying these "extra-canonical" books? Who gets to decide if one of these books should be added to the Bible? What benefit (or detriment) is there for Christians to have only the current collection of books in the Bible?