Understood and agree with the maintenance - I could use mine now without doing anything to it, and I am going for the compressor repair option.
Just by way of considering fixes however, it would be a shame to discount the options available to those viewing suspension problems as we are discussing here. I think I overegged the cost of going coil, its actually less - and much less if I were not to be concerned about retaining terrain response so I've only factored out what I think needs to remain on the car. If going to coil I would have available to sell at least Front and rear air springs at 50 each, compressor 125, bracket 25, clamshells 25, reservoir 50 if all working of course, and I've picked the lower of sold prices on Ebay, it could be more. I'm assuming that height sensors, valves and ecu's would need to remain even after going coil but I'm not certain, if any of that becomes redundant then it further narrows the gap. Dunlop full shock/coil kit or Terrafirma with the smart box to stop error messages etc comes in at 675 less what you can sell. For all that, I am going to stick with Air - but if it were to fail again in the near future its coming out..
Here I found an excellent guide to doing the job for what its worth
http://www.roverparts.com/resources/videos/air-coil-suspension-conversion-range-rover-sport-lr3/
and here is one of the kits, Dunlop BA2236
https://www.ebay.co.uk/i/2533189653...=9044998&device=c&campaignid=974959912&crdt=0