maximawv

I just bought a maxima a few months ago and love it! Although it has awsome performance, I'm tinkering with the idea of increasing the performance. I am thinking about an intake and exhaust with y pipe. Would this make a pretty good, or atleast noticeable difference? I was thinking about the transmission change to get harder shifts, but the guys i work with said it would shift too hard. I have 2 small children that ride in my max, and don't want to hurt them by slamming their head into the car seats. I just wanted to get some input on everyone's ideas about the upgrades.
Thanks,
John