After completing the Gardens for the first time in the first game, you unlock the Create Moon and InfoMoon, and the Narrator tells you to boldly go to them both.
A couple of the unlockable side levels within the game's story mode have referential titles:
One of the DLC costumes is Delsin Rowe, which isn't really a Shout-Out, but just like the real Delsin, he has a pin with the Sly Cooper insignia on his jacket.
There's even a shout out to a few of the Creator Curators of the first game, but it's in Eve's Asylum; apparently the Negativitron doomed them to insanity (even Don's dog!). By LittleBigPlanet Karting, they've come back around.
There's anotherGhostbusters-referencing pin in this game, this one just called "Cross the Streams".
The pin for completing the Dancing Academy stage under a certain amount of jumps is entitled "The Daddy Sack'll Make You...", in reference to Kris Kross's "Jump".