Airfields are real magnets for aircraft, (strange as it may seem
) So if if are using one as a landmark, you can bet your bottom dollar that some else is doing the same thing.
Calling up the airfield to let them know that you are coming through their overhead is a courtesy, even if you are above their ATZ.
They may not be too interested in your transit, the guy down in the circuit may not be bothered either, but the other traffic you don't know about that is also using the airfield as a landmark would be VERY interested. Your radio call is a way of letting other aircraft know where you are and what you intend to do.
So, don't hesitate to call the ground station.