sell the prado

You will have a hard ride and the shocks will wear out faster ...
The first thing they told me when I went to replace my shocks is that I also need to replace the springs,..ati the factory ones are not suited for Africa. I was suspicious that this is BS they tell people so that you fork out tens of thousands of shillings for new springs when the factory springs are perfectly fit for purpose. Ati not fit for Africa! I had carried five people into rough gicagi roads and they functioned perfectly, the wheels didn't touch the housing or anything like that.
Anyway, to shut the dude up, I started going at him with technical questions, like the tensile strengths of the 'heavy duty springs' vis a vis the factory ones. To end the argument, we set both springs in some machine and compressed them to get the readings. Guess what, the difference was negligible, and the factory spring spread back to its normal length much faster than the after market one.
They have never tried to sell me springs again.

spot on! Perhaps the major thing one should worry most is the quality of fuel we have locally, in terms of octane rating, etc. some of the newer engines are a bit delicate in that respect. Recently I also read of Gavin Bennett arguing that modern-day in-car electronics has rendered the need for 'tropicalization' redundant.

I don't understand this tropicalization thing. During the summer, in Europe/Japan they have very high temperatures sometimes even over 35 degrees C, temperatures higher than we ever get in Nairobi. I thought that the engine would therefore comfortably operate in Nairobi where the temperatures rarely go beyond 27 degrees C and 10 degrees on the lower side. I also dont think that the temperature of a running engine varies whether you are in Africa or europe, since the fuel combusts at the same temperature.

To some extent you are right but unless you have full service history of the vehicle you are purchasing there is no way of knowing what engine oil is in there. In tropical areas multi grade oil such as SAE 15W 40 is perfect. This means it can operate comfortably between 15 - 40 deg c. You may find the oil in the imported car may be SAE 0W 30, 10W 30 or even monograde such as SAE 20 or 30.

@mpobiz,..In my case, I did not want the ride height to change (stability and cornering concerns), so the spring had about the same number of loops as the one in the car already, also had a larger diameter. It was a Kings springs or something like that. Sometimes that increase in height is brought about by the spring going on by one loop or half a loop more than the factory spring.
All in all, circumstances differ (different cars, different spring brands, driving conditions), in my case, I found a focused salesman intending to bluster me into buying something I did not need.
I would say that if you carry more weight than average (5 passengers + luggage) in more than 50% of your commute, and 50+% or therebouts of driving is on non-tarmacked roads, there is a case for stiff springs, otherwise factory springs are good for 5 passengers (or less) on tarmac driving and occasional offroad driving; hence spending 50 to 60K on springs is unnecessary.