What would be a "weak" pulldown resistor value? 1 K? Or less?
No that would be strong, weak would be 30K.
However their is no difference in the reading of a sensor not being connected and a sensor connected and no wind. The sessor sends two states high and low, and the digital pin can only sense high or low, so I don’t think it will do what you want.
What are you going to do with the information sesnsor plugged in or not?
This question has been asked many times before and often there is nothing useful a program can do with the information.