David Alexander's hagiography, er, biography of Roddenberry is less useful, but it does include transcriptions of a number of Roddenberry's memos and correspondences written during the run of the series. (Just nothing that would portray the man in a bad light).
Inside Star Trek: The Real Story is still the most definitive book out there. There are mistakes and inaccurate memories -- Grace Lee Whitney and Harlan Ellison both correct its account pertaining to them in their memoirs -- but I don't doubt its overall credibility. Much of it is backed up by multiple sources and archival documentation.