From my mind, there are certainly more: In the Midway Arcade Story level (all your bricks belong to us) you can use the DeLorean or Train to travel to a space station section
-in the maze part of this level go (fly) the lower left, there is an exit that takes you to another mini-game.
-In the Back to Future Story Level you can use the DeLorean or Train to travel to Hill Valley
-In Prime Time tory level there's a room with several 'experimentation bottles' You can use Unikitty to build a dimensional gate from the rainbow bricks you smashed to get to cloud cuckoo land.
-In Portal Story Level, when you meet Wheatley at the ventilation shaft, there is a laser beam protected area. You can get there with Chell's Portal gun and then use the elevator hidden there to get to some extra test rooms.
-Ghostbusters: Before you reach the buildung with Dana's apartment you can use spin-jizu (?) to get to the harbor. Build the bell and call the Titanic.
-same level, final fight (with the 'girl' not Stay Puft). There's a mark on the white stairs where you can use lasers for example with Wonder Woman and open a Portal to Dana's apartment.
-Final Dimension: When you made it through the fire-barrier with water-power there's a place on the left where you can use spin-jizu to open a portal to lego pirates (or so )
I know you can use the tardis in "Riddle earth", and the arcade machine in "Riddle earth" an I think "Painting the town black", but both level kits are still on my wish list. Other than in the US there are hardly any offers (yet?) on dimensions stuff.
So have to split wisely between Dimensions and Infinity
Still hope I could help you