Aluminum doesn't dissipate heat, it conducts it. And if you have an aluminum manifold connected to the cylinder head then the heat from the head is conducted directly to the carburetor connected to the manifold. Even stock cast-iron manifolds can have a passage for exhaust gases to flowh thru in order to warm the manifold and speed the warm-up process in winter. This is the purpose of the heat riser in a stock setup.
I've seen aluminum adapters to allow a squarebore carb to be used with a spreadbore manifold (i.e.: an Edelbrock carb on a stock Quadrajet manifold) and it's been my experience that they produce the same effect as using an aluminum manifold, which can result in percolation.
In most cases it's good to have the intake manifold warm (if not hot) to prevent condensation and puddling of liquid gasoline in the plenum. Cast iron manifolds on inline six-cylinder motors are a case in point...which is why so many old Bolts have a reputation as being cold-blooded.
But it's NOT a good thing for the carburetor to be hot, since the fuel in the float bowls must remain liquid. If the metal body of the carburetor gets too hot, the gas will boil off and empty the float bowls. This is most apparent when trying to start a hot motor, but as 61 Apache stated, it can happen at an idle in traffic. When the vehicle is moving, there's usually some air flow that helps to reduce the temperature of the carb, and the flow of gas is higher than at idle, so the problem isn't so apparent. But while sitting stiil, underhood temps can rise dramatically and fuel flow drops to a minimum. When the gas in the bowls boils off...even partially, it will appear as if the engine is starving for fuel...which it is.
So in my opinion, it's a good idea to insulate the heat of the manifold from the carburetor. This requires something that doesn't conduct heat...and aluminum is one of the best conductors of heat around. So for this particular application, it's not a good material. In other applications, it might be the correct thing, but not here.
