Okay, so you may have seen my thread regarding fixing the EAS on my 94 LSE. Flushed with my success I set about thinking what else might I need a code reader for? I have the on board device, built in, which reads the engine ECU. I have the EAS Kicker. I believe that I can ‘fix’ the SRS airbag by shorting out some pins (there’s an article on that somewhere). As far as I know there is no reader that can help with my seat and mirror memories (a second hand seat ECU has fixed most of that). I managed to remove the Clifford Alarm so that no longer shouts at me ‘Step away from the Vehicle’!
Do any of the other code readers or special tools offer any further assistance? Bear in mind this is pre OBDii.
Not sure what else a code reader might help me with? Central Locking? Manufacturer’s alarm? Brakes? Power Steering? Air con? Radio? I have accessed all of these on other vehicles but I suspect that they may not be accessible on the Classic RR. Does anybody have any insights?

Apart from the air suspension ECU and combined memory seat and mirrors ECU all you really need is a multi-meter. AFAIK there is no "diagnostics" for seat ecu; the internal battery leaks and destroys the board and some of the pins on a couple of the chips. Unfortunately the board has two layers and is not really repairable unless you are an electronics wizz. Replacement seat ECU's are rare and extortionately expensive.
Air suspension fixes are well established.
Engine EFI system is easy enough. A code reader is not essential but quite useful. I use an ECUMate, others swear by Rover Gauge. Both are probably more useful for fuelling problems on catalyst models because you can look at fuel trims but checks with a multi meter can show if the sensors are working but ultimately an oscilloscope is the best tool for that sort of thing or so I am told.
Overall I think I would say don't look for trouble it will always find you in time. If it is working leave it alone, it will break soon enough and just when you don't need it and your code reader is at home.