Hi Jon,
As long as you are not going out of the physical range of travel of the height sensors you could have left them where they were. The 2002-05 L322 has no internal limits in the EAS ECU (in contrast to 2006> where you have a max. calibration range of around 100mm before the ECU throws a plausibility error). As far as airbags failures go, it is usually more an age issue than mileage - dry rot. I def agree on your having accelerated the demise of your airbags with the lift: the area that was normally rolled over for years on end is suddenly straight and stressed completely differently.
I'd be very interested in seeing your spacers. I've thought about spacing the front and rear sub-frames/springs down. Not very hard, though...
(thought about it because I'd love to run a L322 in the
Breslau Rallye if I could find time and money).