The Gold Edition also offers additional multiplayer content, which personally but are not necessary for me. The reason is obvious - the game is no longer new and the mode is used according to little by other users.
Unfortunately, the extra content for the single player mode include any additional missions, or levels of puzzles, as in the Deluxe version of Assassin's Creed Brotherhood. Instead, you get some missions alias served Clay Kuczmarek in the role of subject 16. However, playing style, graphics and gameplay is so very different from the actual game that this additional content actually is interesting only because of the backstory.