Well that's obvious, the intercooler is "outside" the engine bay and the intake manifold is inside. No matter what sort of insulation you put between the intake and the head the intake is still going to be miles hotter than the intercooler.
The question you need to be looking at is whether putting an insulator between the intake and the block drops the intake enough to actually have a positive effect on the air. We know that it has a positive effect on the intake air temperature sensor, but does it actually have any effect on the air. Remember that the intake sensor is going to be mounted on the intake and therefor the casing of the intake sensor is going to be effected dramatically by the temperature of the intake.
I reckon that the difference in the actual intake air temperature will be negligeable.
Easy way to check would be to fit a long thermocouple probe, that way you could centralise the probe in one of the intake runners and the housing of the sensor would make no difference.