Some of these "lost"/apocryphal books are quite apparently fictional works, but others have significant historical value, and even the WTS quotes the ante-Nicene Fathers (selectively and non-contextually)(Should You Believe the Trinity, p. 7, etc) to support Arianism, e.g. Justin Martyr, Irenaeus, Clement of Alexandria, Hippolytus, and Origen. The Forgotten Books of the Bible contains writings by Clement of Rome (a disciple of Peter), Barnabus (Paul's companion), Ignatius (bishop of Antioch), Polycarp (bishop of Smyrna and disciple of John). The sources and associations of these writers (and their writings) is subject to some dispute, but the popularity and general acceptance of many of them as worthy of official church use, sometimes over a span of several centuries, shows the influence they had.
It's hard to get a clear picture of the development of the early Christian church, even with these writings in hand. Without them, we'd be totally in the dark. Well worth reading. They give us a perspective on the fluidity and investigative nature of early Christian doctrine, in contrast to the "we have the truth, here it is, take or leave it" attitude that marks the WTS (along with most cultic movements).
Craig