Oh yes and what part is a myth and which part is only half true?
The myths about heated inlets are that you only need them in the depths of the arctic and that it aids rapid engine warmup. The half truths are generally about the amount of power lost to it and how much heat is transferred to the charge. You are of course quite right that a denser charge has more potential for power and at something like 2.5% increased mass per degree cooler at atmospheric pressure there would seem to be a major benefit available but as ever it's not that simple. I see you've written about what people generally consider to be the carb icing effect. In fact this effect is caused by fuel condensation (actual carb icing is the throttle getting frozen open and the piston freezing) and that is why the walls of an alloy manifold should be warmer than the charge within. Over the few years I've been contributing to this forum we have had a great many members complaining about the fuel condensation problem, it is very common and not just in the arctic. The reason it is so common is the same as the reason that the minimal heat transferred to the charge passing through the manifold has little effect, unlike fuel injection carburation of the charge naturally refridgerates the charge by several tens of degrees. So the inlet is constantly being cooled by the charge and will become very very cold when there is gallons of external air being washed over it at high speed as well. Unlike many other cars the Mini has a vast amount of high pressure cold air being pushed in the front of it when travelling at speed. Fuel condensation also washes the bores clean of oil of course and drastically reduces the life of an engine. It's the shape of the manifold that causes most of the problem as it is quite convoluted. Twin carb manifolds aren't ever heated and don't need to be because they are straight. As you say, port robbing is a major problem with a single carb manifold.
Yes forced induction engines see a major benefit from intercooling but that is primarily to counteract the massive heating caused by the compression of the air.
The temperature of the charge really does nothing to aid engine warmup, as you say yourself a cooler charge has greater mass. More mass of air being compressed would produce more heat and more mass of charge ignited would release more heat. As a result a cooler charge would heat the engine up more quickly, not a warmer charge. People tend to think that the reason the intake uses a hot air oven as standard is also to aid warmup times and again this isn't true. It's used because a carb can't be made accurate across a very large range of inlet air temperatures.
The most important reason to heat it, and the reason that most people I've seen on here should heat in my opinion is regulation of the tuning. A heat regulated inlet manifold smoothes the tuning of the car and ensures there is always more or less the same volume of charge available to the engine. It keeps the engine in the same state of tune whatever the weather and based on the number of people who complain about rough running in winter or the car cutting out when you hit the clutch at a junction after a long run on the motorway or about many other tuning effects I would say that this is the most important thing to most of our members. Many people on here, and in general I believe are concerned primarily about reliability in their Mini and regulating the inlet is a very good way to keep the engine reliable under all conditions. The amount of power sacrificed to it is minimal and as I understand it you don't actually loose any torque, you just move the peak torque lower down the range (hence the power reduction) by heating.
My answer is probably only half truth as well, but then two halves makes a whole answer!
