Intake help?

hi there. i am planning to buy a 2008 scion tc with intake installed by the dealer which is gonna cost me almost $400. i barely have any idea about intakes but just know that it will give me more horse power. my first question is the intake bad for cars? do i need any other modification like struts or anything else if i install intake ? is the car gonna take more gas? how much horse power i may get? thank you in advance for ur istance