Well I'll start by saying that the air to spring conversion was fairly shoddy, the previous owner hadn't set the ecu back to spring and I'm willing to bet he used the cheapest kit going.
I had a local land rover /4x4 specialist convert it back for me - both because I didn't have the time/skills myself or a nanocom to plug in. Luckily he happened to have a 2nd hand compressor which saved me £300 as mine was ceased and probably the reason it was converted to spring in the first place.
Ride seems much improved, slow bumps on the rear seem much more stable and on a quick drive round the woods its noticeably better. No grounding on the tow bar (I did cut off 2" from the bottom with the disc cutter but it still grounded in 1 place with springs) and the few rolling bumps I have to drive over are handled much better.
If you can justify the expense (and if its just air bags then its not mega money) then definitely do it. I'm glad I went back to air and didn't prat about with HD, lifted, springs.
Haven't put the 90kg of tent on yet or tried with trailer full of logs, that's for next weekend!