Here's an interesting idea from the 'Vette people: a dual-mode exhaust. Flip a switch, and it goes from a quieter exhaust to full-performance roar. Old press release here:
Jalopnik - Yeeha!! 2008 Corvette Gets Big Boosts of Both Power and Torque - 2008
Will there be a similar system for the Z? Could be especially useful for those of us who want performance upgrades, but the cops hate the roar...