i can only speak from personal experience, so this isn't representative. my E70 has close to 100k (160tkm) on the clock now and so far the suspension is going strong, apart from wear & tear items like bushings & stuff. i used to break rear springs on my trusty old E36 pretty much on an annual basis, without particularly spirited driving. i also managed to mess up and having to replace both bellows (air springs) on the E39, which had about 100k on the clock at the time as well, just by lifting the rear off the ground to replace the brakes. after a certain age they really don't want to be extended, so i'm waiting for those to go wrong on the E70 in the not too distant future, something you'll have to deal with sooner or later (me too, yikes) if you have air suspension in the rear. the compressor works pretty silently, i barely ever hear mine, so i wouldn't be too worried about that. but the fact that the rear holds up is proof that it's all (still) working. pneumatic systems like these will always leak air, molecules can also leak through the rubber of the bellows over time, same as they would with a tyre. if your compressor suddenly stopped working, the rear of your vehicle would start sagging pretty soon and the car will eventually become virtually undriveable. as for replacing the suspension on your own, i've not done it so i'll hold my advice on that.

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