No it is not. If you had an 04 or earlier models then yes.... The reason you would have changed out the up pipe is because of the cat that Subaru used to put in them... They got rid of that though, so it is not nessecary, even if you were to upgrade the turbo it still is not a must, though nice.
That being said it is a pain in the a$$ to install, so I would recommend it.
Yup, u can change the uppipe without an AP......it'll help with the turbo being able to spool up faster. In essence, more responsive! .......and yes, It is a pain in the a$$ to install, u MUST have a lift. Using jack stand is useless!!
actually the stock UpPipe looks about the same size as an aftermarket one. maybe bigger??
there are no sensors built into it. here is a picture, the heat shield makes it look huge.
i will have to look for the picture comparing the pipe diameter when i get off of work.