My 2001 DII has the rear air bags and 2" spacers.
I like the system and it performs well on the trail however I don't trust it in the long haul. I have a new set of extra heavy duty OME springs from Expedition Exchange sitting here ready to replace the bags either this week or next week. If you have any questions on the swap just call Ho at EE and he'll help you pick the right springs for your use.
I've had one airbag blow on me, while running El Camino del Diablo, and limped home 250 miles with a couple of wood blocks as a spring and ratchet straps as a shock! - I actually got up to around 60mph on the highway.
I had another bag just leak while in the driveway.
Since then I have carried one spare bag all the time and two spares on trips.
I like the way the bags adjust to keep the vehicle level regardless of the load and you can press a button to get an extra 2" of lift on demand.
For me, swapping to coils will give me one less thing to worry about.
Brian