Lance Parkin wrote an essay called "Canonicity matters: defining the Doctor Who canon" for Time And Relative Dissertations In Space, a collection of peer-reviewed critical academic essays on Doctor Who, but it is just as relevant to Star Trek and our conversation here:
"The key to understanding the importance of 'canon' to a Doctor Who fan is that it represents investment. Fans spend a great deal of time and money on Doctor Who. The average Briton buys three books a year. At their height, there were that many Doctor Who books being published every month. Doctor Who fans are not lost in a fantasy world -- they have as great an understanding of the circumstances of television production as any other group of viewers. Via the Internet and conventions, they have far more direct contact with the authors of the novels than any other group of readers. For this level of commitment to work, they have to know the stories matter. Fans want the writers to demonstrate at least some of the care and attention to detail that they possess. For the emotional, time and financial investment of being a Doctor Who fan to pay off, they have to contribute to and inform, in some way, the wider Doctor Who universe. They -- the stories and the fans -- have to matter."
I think this applies doubly to "nonfiction" sources like technical manuals. If you read a novel and it's not "canon", at least it's (hopefully) still an enjoyable book-- the reaction to the Crucible trilogy was along this line. But a technical manual doesn't provide that sort of engagement; you read it to learn about something, you read it to learn "facts" about your fictional world. And if those facts aren't consistent with what's gone before or adhered to by what comes after, then what's the point?
"The key to understanding the importance of 'canon' to a Doctor Who fan is that it represents investment. Fans spend a great deal of time and money on Doctor Who. The average Briton buys three books a year. At their height, there were that many Doctor Who books being published every month. Doctor Who fans are not lost in a fantasy world -- they have as great an understanding of the circumstances of television production as any other group of viewers. Via the Internet and conventions, they have far more direct contact with the authors of the novels than any other group of readers. For this level of commitment to work, they have to know the stories matter. Fans want the writers to demonstrate at least some of the care and attention to detail that they possess. For the emotional, time and financial investment of being a Doctor Who fan to pay off, they have to contribute to and inform, in some way, the wider Doctor Who universe. They -- the stories and the fans -- have to matter."
I think this applies doubly to "nonfiction" sources like technical manuals. If you read a novel and it's not "canon", at least it's (hopefully) still an enjoyable book-- the reaction to the Crucible trilogy was along this line. But a technical manual doesn't provide that sort of engagement; you read it to learn about something, you read it to learn "facts" about your fictional world. And if those facts aren't consistent with what's gone before or adhered to by what comes after, then what's the point?