I've seen someone asked about this but it says because of the brake rotor, it won't fit? Mine is a 2005 G35 base sedan. Correct me if I'm wrong, but is it there are more tire choices for 16in wheels than 17in? Thats what I'm thinking of and also its a bit cheaper too.

 

Are you looking to have it with winter tires? 16" will fit over base brakes diameter wise, just be careful with offset. I had 16" black steel wheels at some point, but do not remember the specs.
As for alloy wheels-don't do it, it will be ugly-just like wearing pants which are too short . Stick with OEM wheels.

 

Nope, not looking for snow tires. Because I have another car with 16" wheels and when I look up on Costco website for options of tires, there are more to select from than 17". Guess if I were to get something different, I will need to go somewhere else then...