For now, give this a shot and see what kind of a difference you notice. Most of the things that affect the mileage have already been done. However, you may have the fuel pressure checked. If the fuel pump has weakened, to compensate for the lower fuel pressure, the ecu would increase the duty cycle of the injectors, causing the mixture to get rich and consume more fuel. It would be ideal to keep the fuel pressure gauge connected and drive the car for some kilometers and observe the fuel pressure at different situations, like when driving on a straight road, while driving with the ac on, while driving on an inclined road. The fuel pressure should not drop much in all of the above conditions. I've observed the correct fuel pressure to be around 3-3.3kpa.