The Historia Augusta is pretty much an elaborately written satirical gossip-book of Roman imperial families, with the second half of the volume bordering straight fabrications and fantasies. I'd admit that they are highly enjoyable to read, not least because of their often comedic nature, but also due to the fact that many of those made-up anecdotes have become so embedded into our own reception of the Romans -- from Tadema's painting The Roses of Heliogabalus (an absurd-ish tale only testified in Historia Augusta) to the popular imagination of Rome's fraught relationship with Jews as exemplified by Hadrian's ban on circumcision (an account first documented in Historia Augusta and remained a controversial topic to this day), it's quite surprising to see how much of our contemporary perception of the Romans is actually borrowed from such an (historically) unreliable source.
That being said, the main values of Historia Augusta does not lie in its historical authenticity, but rather in its representation of Roman elite thoughts towards contemporary politics and social issues. In this regard, Historia Augusta did provide modern readers with a lot of stereotype-defying images of Roman aristocrats, among which are its overt pro-pagan rhetorics and sarcastic treatment of the Christian faith. As an non-professional reader who's chiefly interested in exploring the less-known corners of history, I find this book demonstrating to me the versatile nature of Roman literature and intellectual thoughts. Recommended.