It's worth noting that the coil spring suspension actually holds cargo and/or tows quite well.

I'd say that the primary benefit on the E53 is probably actually ride quality, and you really want the 4-wheel air for that. (I've considered it, but haven't been sufficiently motivated.)

Attached Images

 

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2011 M3
2006 Sierra 2500HD 4WD LBZ/Allison
2004 X5 3.0i 6MT
1995 M3 S50B32
1990 325is
1989 M3 S54B32

Hers:
1989 325iX
1996 911 Turbo