After some consideration here and there, I think I will go for the spoiler for my Z.
I did seriously consider the exhaust but after my Z ride on the past Wed, with the top down, I am a bit hesitate about hearing a louder exhaust note everyday, also conversation inside the cabin even with the top up... And the CAI is starting to giving a nice engine note...
So.. after all the thinking, I will go with spoiler...(maybe for now.. LOL)