[Olympiadis]

With a properly working OBD1 or OBD2 system it shouldn't matter if you have a MAF, MAP, or both.
The MAF and MAP are key in the fueling equation that determines what part of the fueling map the ECM uses; however, the O2 sensor always has the final say in determining the injector pulse-width that is executed. The adaptive fueling routine is applied last and calculates any fuel trims necessary to the final pulse-width value in order to stay within proper AFR range as determined by O2 sensor feedback.

It is true that many systems out there are not functioning 100% correctly, and so you will get many variations on your results.

The WAI does work on our 03 Focus, and especially so in cold weather.
As mentioned in an earlier post here, the loss of power (throttle response) due to the warmer air will indeed increase throttle resolution, thus making it easier to drive the vehicle while using the least amount of power necessary.
More throttle resolution means more gas pedal movement for less opening of the throttle blade. That can be a big help on some vehicles depending on the mechanical leverage of the throttle cable connection, and the internal design of the throttle bore. Some throttle bodies are designed for very snappy reponse with little throttle movement, and others are designed to be much less sensitive at very low throttle openings (right off idle).

WAI systems that I have tested in the past have worked extremely well on carbureted and TBI systems where fuel vaporization and distribution are poor.

As for pumping losses, I'm sure they are a little less in some cases, but I don't feel that is the primary source of fuel economy gain by using the WAI.
It seems to me that the heat increases the quality of fuel vaporization, and speeds up the burn in the chamber.

I have seen an instance where a WAI caused a significant loss in FE. It was an underpowered engine that was needing to do a lot of work, - load carrying and hill climbing. The loss in power from the WAI created a need for so much throttle that PE - Power Enrichment mode was invoked by the ECM, which enriches the mixture to between 11.5:1 and 12.5:1 AFR depending on the model. In this case it would have been extremely helpful to have a driver controlled valve to switch between CAI and WAI.