The later version of WORLD actually cut a lot of good stuff, and the new material was a lousy trade. I went back to the 70s pb shortly thereafter.
I'd add Gerrold's TROUBLE WITH TRIBBLES making-of book; it was the first nf trek I read, even before WORLD and MAKING, and it has good info.
And just to call into question some of the INSIDE STAR TREK stuff (not all of it, but so folks don't just buy it as whole truth), I'd suggest finding Ellison's book on THE CITY ON THE EDGE OF FOREVER, which clearly not only makes Justman and Solo's recollections suspect, but also their overall credibility, since they never made corrections even after being reminded about their errors.
Also, if you apply the idea that at least some of what happened to Ellison's script -- like the secret that DC Fontana rewrote it, something she denied IN PRINT in CINEFANTASTIQUE about 20 years ago -- also happened to other people too, then it really makes you wonder about the how and the why of it all.
Gerrold's TRIBBLES book mentions how Norman Spinrad thought DOOMSDAY MACHINE had been ruined by rewrites (then again, Spinrad also managed to get another of his scripts KILLED by asking GR to trash it after Gene Coon turned it into a comedy. hey, I'd be happy to have Gene Coon rewrite everything I've done in my whole life, because that is one guy who seemed to really solve problems. )