Waxing your car makes a difference, but it is so small that you would never notice it.
To put it in perspective, an F1 car gets waxed before a race and even the panel gaps are taped to reduce drag. This yields a 0.05 seconds saving per lap. One lap is about 3 miles long, but races are typically around 65 laps so the advantage is about 3.25 seconds. Every little bit makes a difference.