Deal pal! Washing cars in this weather is hell for sure and not fun.
Yeah the 350z visually longs for 19's imo, I won't go for sticky Michelin's or similar as with the 19's I won't push the car to the measure that they'll make a noticeable difference. Reason being the car feels slower in all regards, so why push on in a slower spec. It's like racing someone in a new car with the drive mode set to normal instead of sport, why bother? Or from the days of Blitz boost controllers, racing in B boost instead of A. New rubbers all round will be great of course but no need to spend extra imo for the sake of it.
19's for Show, 18's for Go this you will attest to also.