There was some member a while ago that lived in Hawaii that replaced his X-Reas at about 50K. I don't think he had the air suspension.
I have heard they have shocks that bolt right up to the factory brackets now.
One member used the online store "Shockwarehouse" and said they were very helpful. They do not list X-Reas on their site, you have to call them.
They are at -
http://www.shockwarehouse.com/
Most who have done this have said ride and handling improved a great deal.
I have an '05 with the X-Reas. Knowing what I do now - I would run the other way rather than buy a 4Runner with the X-REAS.