Simon, i followed your link to this thread from another.
I have a good LC5 which i found just over 2 years ago if i recall correctly, and am very happy with it, that too had been lucky enough to have well heeled previous owners, and the rust underneath was minimal, apart from the bash plate which was holed on the edges and is now replaced with one of those cheap (but not half bad) underbody plates from Romania.
Anyway, you mentioned the suspension above, i'm happy with the set up, i'm running on Yokohama GO15 tyres which are winter rated all season road biased AT's, and i'd be very reluctant to lose the sure footed wet handling of the car especially, which i put down to the rear air suspension as much as anything, i tend to run in the setting below 'sport' (pause for snort of derision, please Toyota sport and an LC are not happy bedfellows), which seems a good all rounder for me living as i do in Northants and having to drive the cart tracks otherwise known as roads around here!
Will have a ££ decision to make should the tems shockers start to fail, but changing the rear airbags looks easier than swapping even a spring over.
Which brings me to this video, because not many videos about on how to swap the rear airbags, this video is of a Toyota Sequoia airbag swap, essentially the same set up as LC5, but the chap goes into detail of where to disconnect the pipes for an easier life which other videos don't, might be worth bookmarking in case an airbag swap is needed.