A lot of us here have walked this road several decades ago, where variations of rolling stock were "documented" to the N-th degree. For example, whether a box car door was one color over another, or a decal was black on one car but white on another, etc, etc... To this day, I wonder whether these items were documented just for the sake of documenting by those who loved the hobby of collecting... or whether it was all a ruse to set higher prices for those variations consider to be more scarce than others. 
Boy, both of the reasons you give have a fairly negative tone in my opinion.
I don't think anyone goes to the trouble to document variations just for the sake of documenting.
When true collectors do in-depth studies of particular items, its because they are interested in them. Lucky for the rest of us, they are willing to share their observations with the rest of us.
I think there are people who either do their own studies, or more likely just leverage the studies of true collectors in order to set higher prices.
And the price guide publishers certainly benefit from the identification of variations and price shifts because these events help sell new editions.
What is over documented to one person, is fascinating information to another.
I never let price guides, reference books, or others in the train collecting community tell me what to collect. I've always collected what was of interest to me, and paid what I thought was a fair price, based on my experience.
