The problem with tuning with minimal mods ie just Intake, you've only potentially derestricted the factory intake [Mugen intake should be an improvement from what I've seen] however on the other side of the power equation, the factory headers & exhaust [possibly your compliance CAT too] are bottlenecking the potential gains to be had by the intake. Result is the tune will only give you a more aggressive mapping against the factory's usually conservative tune.

Like NeedVtec mentioned, there are exhaust [Headers don't amplify sound as much as exhaust] that are quite civilised like the FGK Legalis-R [Link] and the FGK RM01A [Link] is louder but not by that much =)