My 2007 Expediton had the Air compressor go bad, and I replaced it with one from Suncore industries, that one seemed to die recently, and I suspected that it was working too much or too hard due to a leak, in any case the rear end sagged down and I was down to the bump stops.
I purchased a coil spring kit from Arnott (just the rears) and recently installed it myself .... not too bad a job if you can do brakes .... I did it in my own garage no lift just jack and stands...
In any case my early verdict is I am happy with the rear height being back to stock and the ride of the vehicle is very good again. I won't miss the air suspension troubleshooting. It was nice while it worked, but I like the setup now. Good luck!