Yes, at that low wind speed there is not much power available. But remember, at double that speed, there is EIGHT times more power. Calculations based on average speed are only valid for a linear power-speed relationship. For a wind turbine, it is a cubed relationship.
The advantage of generating power is that it can be generated in one place, and used in another, unlike the windpomp.
Mounting a compressor is a great idea - the air can go via hose to be used somewhere else, like electricity. Could use the air for pumping water directly... Trick would be to measure the torque required, and match the blade size, shape and TSR to that. What is the normal RPM for that compressor?