Hi sake-bito, I've driven 16 350z's, and been a passenger in more. Both manual and auto. Honestly you don't sacrifice much having an auto. I'll normally blitz the manual guys off the line in either manual or auto mode, and my braking points are similar to manuals, that's purely driving style, being reasonably aggressive, and driver experience. In terms of drivetrain loss, only marginally more than a manual. The transmission is very smooth, and responsive, everyone comments on it. In extremely heavy traffic being able to switch it into auto mode is a leg saver. If you drive mostly in auto mode of course you'll use a bit more brake pad, but not hugely so.
When I first got my Zed 4.4 years ago, I was driving in extremely heavy rush hour traffic and traversing the city all day in heavy traffic, it saved my sanity.