shanegtr - some interesting points you raise which I predominantly agree with. Modern vehicles offer so much more in terms of performance, handling, safety and capability, plus build quality and engineering in most cases has improved dramatically.
One of the challenges here in Australia for us 4WD people who want to travel remotely is how harsh the conditions are, and much different to those found in most other countries apart, perhaps, from parts of Africa and South America. Also, the remoteness, particularly from towns and assistance, is not really matched anywhere except perhaps Siberia. That poses unique challenges.
On the diesel vs petrol issue, that's a tricky one. One of them is the risk of picking up water and other contamination in fuel in remotes spots. This is most dangerous for diesel. In speaking to a well regarded diesel specialists, he told me of many instances of travellers' and farm vehicles requiring major, expensive repairs from ingesting contaminants. A Discovery 2.7TD that required $17,000 worth, a Landcruiser not much less, various ordinary utes and traytops at around $8,000. The problems affect older more basic engines too, but a bit less so because of the lack of high pressure fuel systems, but the cost to repair is lower too because of fewer, cheaper parts.
His advice? Either fit a premium quality water separator/filter system and check it/maintain it religiously, and have the car properly serviced regularly by knowledgeable people, just accept that diesels require more servicing and care, particularly as they age. Or else, buy a strong petrol engine vehicle, add an extra filter and a long range tank and pay a bit more for petrol, but save on servicing and lower maintenance/repair costs.
Particular models, such as the 3.0 turbodiesel Jackaroo, some Toyota engines (one series of Prado D4D and the early V8TD Landcruiser, some Hyundai/Kias, Merc diesels in the earlier Jeep Grand Cherokee and others, these are just examples) have proved troublesome. But overall, modern engines were well made and reliable, and the biggest risk for offroaders was the water issue and lack of quality maintenance. And he said that from a business point of view, he was very pleased to be in the diesel maintenance trade!
Many people have great experiences with their modern diesels. A chap in the UK who deals in and moves classic cars did 540,000 MILES in his Disco 3 2.7TD mostly towing a car trailer which was often well loaded around UK and Europe), before needing a top end rebuild (he replaced it with a new engine and did various other items while there, then kept using it). On Landrover sites I have seen many with more than 300,000kms+ largely trouble-free. You will find similar example on other brand forums. Not surprisingly, people who do high kms tend to prefer diesels.
On the other hand I have just sold our 300,000km old 2000 Astra auto to a friend, a great little car that drives really well, feels tight and is reliable. It had a rebuilt head at 270,000 after a blown head gaskets, replacements of brakes, shockers, O2 sensor, aircon compressor and a few little electrical gremlins. Feels like it will do many more kms and interior almost like new. Have another at 200,000kms that feels great too.