The Lonely Planet answers the question, ‘why travel such a distance when you could fly’? It suggests that compared to the cramped confines of a flight which merely delivers you to the starting point of your holiday, a sleeper train is a memorable travel adventure in itself. According to LP, this is particularly true for the Indian Pacific, which is one of the world’s few transcontinental trains.
Source: Coast to coast: across Australia by rail aboard the Indian Pacific
I’ve only had one multi-day train trip and that was the Rocky Mountaineer in Canada’s British Columbia, which was a once in a lifetime experience. I guess that the Indian Pacific must be compared to the likes of the ‘Trans Siberian’ but I think that I’d get restless and a bit bored with the repetition of the scenery. Also the more comfortable classes are rather pricey, so it’s down to personal choice.