Just to be annoying, I'll put this thread back on track (although I'm not sure if I succeed) :D
Jennifer Lynch said she was told who the killer was and she wrote some hints in the diary but she had to remove some text from it as the hints became too obvious. The way BOB was written in the diary was approved by David Lynch and Mark Frost. The killer was known and I think one of the hints was the part where Laura writes something about not remembering if it was a dream or not but Leland had said some dirty stuff to her.
The most fascinating thing about Leland and Bob goes away when it gets treated as "just a demon from the woods" or "just a metaphor" thing. Bob can be both at the same time and I think he was supposed to be like that. After all, they knew who the killer was before they knew anything about Bob so I think it's quite odd to think that whatever they had thought Leland was all about was put aside as they "found" Bob. I can't imagine Mark and David going like "ok, Leland was a man who sexually abused his own daughter and eventually killed him but let's forget that and change it with this thing about a possessing demon doing all the bad stuff" :D
And what comes to the portrayal of Bob in the diary, I think it was very entertaining, creepy and gave a lot more character to Bob.