The ancient heretical books are interesting if just for their historical value. To understand the various Gnosticisms (Gnosticism wasn't a monolithic heresy) seeing the works they produced is incredibly important.
The Deuterocanonicals are, of course, very important because most Christians still regard them as Canon. They are, at the very least, exceptionally good to read, edifying, spiritual books that not only have important historical value (e.g. 1 Maccabees) but great godly counsel.
I would also regard the Antilegomena (disputed books that were sometimes regarded as Canon and sometimes not, which technically also includes books we now regard as Canon such as James, Revelation, Jude, 2 Peter, etc) such as 1 Clement, the Didache, etc as good and beneficial to read.
The ancient pious fictions, such as the Infancy Gospels are interesting, if only from an amusement perspective. The Infancy Gospel of Thomas (not to be confused with the Gnostic Gospel of Thomas discovered in the Nag Hammadi Library) contains somewhat humorous stories such as St. Joseph cutting a wooden plank too short, and the Child Jesus stretching it out to the proper length. Some of these stories, while regarded as amusing, somewhat humorous late antiquity pious fictions in Christianity, are actually retained in the Qur'an and accepted by Muslims as scriptural truth.
-CryptoLutheran