Originally Posted by LunaZ

You can most certainly add hundreds of dollars worth of sound deadening material to the car. Gut the interior, pad it, Dynamat it and whatever else works, then put it all back together... or pay someone to do it.
You can shop for the quietest tires on the market and replace the stock Potenzas.
At the end of it all, it probably still won't be quiet enough (as illustrated by the disappointing results experienced by some posters) and you will have spent a lot of money and time on trying to make the 370Z something it's not. It's not a BMW, Audi or Lexus. Take out the "performance" part of the equation, and you're left with a simple matter of economics. I'm sure it costs less to skip all the sound deadening measures that are incorporated into the aforementioned luxury brands.
If a quiet cabin was high on your priority list when shopping for cars, you made the wrong choice, plain and simple.