I have a 95 Classic SWB and the air suspension had already been removed and coils put in their place. I don't know how often the air suspension needs to be serviced or replaced, but I know it is very expensive. My guess would be that regardless of how often you are raising and lowering the vehicle, it will still be bound to break eventually because the system will constantly be monitoring and adapting to the road conditions to deliver a quality ride. I don't know if the range rover/land rover you are thinking of buying will require expensive replacement parts, but I know the alternator for my rangie was over $700.00 new from the dealership, and not much cheaper from other sources like atlantic british. The dealership told me parts for my vehicle were so expensive because it shares many parts with the Defender, which is not sold in the US and by their logic more expensive sonce they have to be shipped???
Anyways, in short the air suspension will be expensive to fix or replace, and most people convert to springs. And other repairs can be expensive, but I find the general maitenance to be pretty easy, and I am not a mechanic by trade. It's a great vehicle in my opinion though!