I got a 2002 RR after having a number of Disco I's and 2's, and while it was one of the best cars I have had, it was a money pit and got shot of it after it spent most of the time I had it off the road with suspension and electrical problems. I had it 6 months and drove it no more than 2 out of the 6.
I bought it knowing it needed ball joints, discs [pads etc, and these were easy wnough to sort out, but then the air suspension played up, and eventuially I had to spend over £1500 converting it to coils, then it developed electrical problems that kept killing batteries, then finally I had to replace a single injector at about £400. At about 100k, the auto's begin to develop gearbox issues if they haven't been looked after well, and I've also heard of turbo failures. Neither of these ahppened to mine to be fair.
I went back the way and bought a manual diesel P38 (not everyone's favourite, but with the exception of a perished cranckshaft pulley that car never missed a beat in the 18 months I had it. I had a tuning box fitted and regularly had 30mpg out of it (more on a run) and it pulled like a train.
I went the RR route because I was concerned about the bad reports on the D3's (and the cost), but earlier this year I bought a well maintained D3 from a fellow club member, and have racked up 10,000 miles since February, and it's been fine. I really think the secret is looking for one that's been well or over maintained, and I would be less afraid of the D3 than the RR TD6. I also think the D3 is a far more responsive car to drive.
Hope this gives an insight.
PS I've still got an older Disco 2 that I've been rebuilding which I'll probably use for off roading rather than getting too adverturous with the D3.