Now that I have a copy of the first edition from 1972 as well, it's interesting to compare and contrast. I sense that Dicks took a pretty heavy hand in rewriting almost every chapter of Hulke's original text, sometimes from scratch, sometimes (the chapters on the Daleks and "How To Make A Monster") just with a light touch of editorial improvements. Gone is the nonsense about the Doctor's real name being ∂³∑x², let alone the bizarre postscript from the Rev. John D. Beckwith, Chaplain to the Bishop of Edmonton; but in comes plentiful cross-referencing to the Target novelisations, which of course were very new then and had not been around at all in 1972.
There is huge nostalgia value to it anyway, but I also think that for what it is trying to be, it is still a good book, and the foundation of Whovian reference books ever since.