In order to be unessecary specific:

if it would benefit the waves:

it would only benefit the outgoing waves.

The waves coming back feom clients, transmitting data back to the wifi access point would have to fight against this additional airpressure.

But this is all only hypothetical and i am sure in the real world it would make no difference even if there would be a benefit in theory.

And yes you are correct the electromanetic field of the spinning fan would definitly harm and not improve the signal quality.