As Paul says, dont be too worried about the 2009 Satnav, its not the best. I waited out until the MY2010 models were announced to order mine specifically for the new uprated satnav and entertainment system upgrades that they got here in the US too. The 2009 one you have to use AUX in for iPod and the unit doesnt control the iPod.
MPG always improves after the car is run in and a oil change or two so dont worry about that either.
I agree with the 350z feeling more sporty, it was just a bit more of a brute, but the 370z's new refinement and upgrades more than make up for the small loss of brutishness.
With regard to the exhaust, I know what you mean. We have a member on our site who has put a Stillen CBE on and it makes such a big difference, pretty similar to a Nismo on a 350z, very nice sounding. I have one sitting in my loft for when my car arrives. The chaps at Stillen are brilliant and it was no hassle importing it (and a Gen 3 intake). You can see Colins thread on his exhaust here -
350Z-UK.COM The Nissan 370Z Owners Club • View topic - Exhaust and wrapping done