to be honest i think the majority of wings out on the market are cosmetic and have never even been tested or proven to provide maximum downforce with minimum drag.
but yes if they did actually work the way they work on race specified vehicles, then they would benfit FWD vehicles as well. Regardless of where the drive wheels are located, it would not be beneficial for a part of a vehicle to raise in the air. Look at the Trans-Am Series or the LE Mans 24 hour. I bet not all of those cars are rear wheel...... I have seen honda civics run the touring events, and yes those events are production cars that have been gutted.
But on the other side f the coin, the average driver will never get up to speeds that would make it worth the time and money to put a wing on it. Hence they are for cosmetic use.
I still want one.... it should be here in a day or 2 by the way.