The air coming off your CPU heatsink shouldn't be hot enough to overheat the RAM. In fact it could be cooling your RAM if your RAM temperature is above that of the air coming off the CPU heatsink. If the hot air is in fact causing the problem, RAM heat spreaders would not help. They aren't a magical devices that make things cooler. They just increase the surface area so that the heat coming off the RAM comes into contact with more air. They could actually cause a reverse effect by exposing more surface area to the hot air coming off the CPU, if that air is hot enough to heat the RAM.
I say you isolate your problem by plugging the parts in question into another system you know that works.