I think many of the reliability issues for the Ranger Rovers centre around the diesel engines, which have a number of known issues. The petrol engines are much more reliable albeit somewhat thirsty. I bought my 4.2l Supercharged First Edition RRS nearly 7 years ago when it was 3 years old, so coming up for its 10th birthday and it has been fabulous, a truly amazing piece of kit. The only thing that has gone wrong is the air suspension compressor and a few associated parts and a replacement lower wishbone and track rod. These are all known wear items and typically need replacing around the 60k mile mark, which was the case for me. Replacement parts are more robust and so should last longer. Other than that it has been rock solid and goes incredibly well for something that weights nearly 3 tonnes!
For me there is no comparison to a Volvo, which while very comfortable has nothing like the performance or the off road ability. A Cayenne is better build and finished and a Turbo would certainly leave me struggling to keep up on road, but off road and in really poor weather/snow, the Sport would come in to its own. We drove back from France this February half term in a blizzard and due to a blocked French Autoroute went via Switzerland. At one point we were on a two lane road with 4 wheel drive Audi drivers, both A4/6 and Q7 struggling with snow chains to get up the hill, the RRS didn't even break sweat. When we were the only car we saw for miles on a very snow covered road the RRS felt completely stable and in control, I am not sure a Cayenne or much else would have made such easy and quick progress.
For me I cannot ever imagine selling my Sport, it is very comfortable, has seriously impressive performance, handles reasonably well given its weight, and will go just about anywhere. Plus it is built like a tank and feels very safe. Second hand the first gen Sports are now starting to look like very good value, just make sure it has been serviced properly and the suspension been sorted and you should be good to go!