Let me make a list of all the scientific research that proves that aerodynamics don't have an effect until 60mph:
List
End of list
Wait, if we modify the statement a little there is some evidence that at speeds below 60mpg aerodynamics don't have any effect... if you drive on the moon of course. And above 60mph they don't have an effect there either.
Sorry, no offense. I just had to make a joke.
I do get the general idea of what people are getting at. Aerodynamics don't have as much of an effect at slower speeds as they do at higher speeds (in Earth's atmosphere or in any other fluid). But on the other hand, the extent to which they have a noticeable effect and whether that effect is worthwhile or not depends on both the vehicle and driver in question.