The option is there to just buy the new stuff, I don't understand what you mean by "they are expected to buy them over if they want the extra stuff". if you want extra stuff, you have to buy it. If you don't want the extra stuff then don't buy it and get the standalone DLC.
That doesn't include the shader, emotes etc
People might want that stuff to be more unique in the game but they don't want to rebuy the game they've had for a year. Collectors editions are for fans and fans have been playing for a year and don't need the base game and first two expansions. Putting it in that bundle feels a little like they are simply trying to milk more money from people unnecessarily. I wouldn't be surprised if it becomes a thing to kick people from the fireteam who use the new emotes as sort of a protest of spending the money on the cash grab collectors edition. Especially in light of the recent interview where Luke Smith basically talked about the players as a wallet and not a member of a community.
Honestly It would have been so simple to offer a sku without that stuff and lower the price a bit, especially on the digital edition.
The collectors edition in physical format costs $80 and comes with the following. Note, the items in bold are the stuff people already bought last year. Why can't they release a $60 edition and eliminate those? Here's where it gets worse. The digital collectors edition is still $80 but you don't get the steelbook, the artifacts, the cayde-6 book, or posters etc. Further the taken king is $60 and includes last year's content as well. Why? Why can't people just buy the part they don't have? Proof in the following link. Notice there is no option to purchase just the new content.
https://www.destinythegame.com/taken-king/wheretobuy
Destiny: The Taken King Collector's Edition Includes:
The Taken King, the next evolution in the Destiny universe
Destiny
Expansion I: The Dark Below
Expansion II: House of Wolves
Collector's Edition SteelBook Case
Uncover Cayde-6's Intel Cache:
Modified Treasure Island Book with Intro Letter from Cayde-6
Cayde-6's Personal Notes and Illustrations
Collection of Relics and Artifacts
Strange Coin Replica
Weapon Schematic
Upgrade your weapon arsenal with an early access weapons pack. Guardians will receive a Vanguard themed Auto Rifle, Pulse Rifle, and Side arm.**
The Taken King Collector's Edition Digital Content: Includes three Exotic Guardian Class items featuring XP bonuses, three class-specific emotes, and three armor shaders to customize every Guardian class.