So are we saying an $80k landcruiser offers not much more than a $45k Challenger apart from a bit of space and 500kg more towing capacity that you will most likely never use?
I'm guessing by this thread, and the "why would anyone buy a manual" thread, that you are either in the market, or are trying to justify to yourself or others the vehicle you just bought was a good call?
Sure if you look at a specification sheet there will be not a lot of difference between a $40k Hilux and a $20k Great Wall. If you do a lot of remote area touring that extra $20k you spend on a brand that is known for reliability and/or good service availability may be money well spent. See how you go for service and support for your Great Wall at Andamooka.
Also as GeeTee mentioned, you have to take into account if the vehicle suits you. When I was in the market for a dual cab a few years ago I had to strike the Triton off my list as my 6'1" fat bastard frame just didn't fit in it, which was a shame as it ticked all the other boxes.
From an engineering perspective the primary reason for such a price difference between a Mercedes and a Great Wall, putting aside physical construction and material costs, is quality assurance. The reason why a Mercedes dash switch costs so much is because a dash switch design is tested for a million operations before being mass produced. Sure the Great Wall dash switch will perform the same function, but the probability of it lasting as many operations as a Mercedes unit is much less. It is the quality that you are paying for, not just function.
The law of diminishing returns doesn't really apply here. You are trying to say that the more you are spending doesn't yield you more rewards. Like I said before, you are paying for the quality of the product, which is quantifiable and justifiable.