(I've never visited Disneyland Resort, Tokyo Disney Resort, Disneyland Resort Paris, nor Hong Kong Disneyland Resort, so don't be fooled when I pretend to know what I'm talking about. [But I'm pretty good with the information, if I do say so myself. And you can hit me all you want with Walt Disney World.])
If there is any attraction that should be brought over here from Disney World, it is definantely Mickey's Philharmagic for Fantasyland, and if Disney had room, they probably would have Rock n Roller Coaster at DCA for HPB. Pretty much what JarrodDDragon said. It would make both parks a little stronger and fuller.
Rock N' roller coaster was originally gonna be in HPB, but was shelved in favor of tower of terror. Then it was planned to be on the timon lot, and we all know what happened with that. rock n' roller coaster just isn't destined to be in DCA