Had my P38 chipped (Rimmer Power Box) shortly after buying it five years ago, never regreted it. Converted it to springs too, about two years back. Initially it seemed like a different ride, but soon got used to it - and to the fact that it can only sag on one corner if a shock goes (in the middle of nowhere). It is virtually undrivable when it collapses onto its rubber suspension stops with a failed air system, and you'd better not have eaten 'cus it'll shake you to bits for the few miles you can stand it. No, at circa £120 each for each corner sensor and £600 quid for a complete valve block (can't replace them individually) I'd not spend time or money (loads of it) if it starts to play up in this area. I don't usually pay for jobs to be done, but I indulged myself on this one and paid £600 to have the spring conversion ('Footloose', Peterborough). I think it sits up better on springs, though you can no longer lower its height for granny to climb in.
I think you have to be prepared to do a certain amount with a vehicle like this, if only servicing (oils etc.), but I know what you mean about not wanting to balance gear boxes on your head any more (not that you could with these).
Year 2000 on seem to be more reliable in the electronics department (a notorious source of frustration.
To me, it's a Landrover, a Range Rover at that, and it has to be worth it.
DougK