I was having heating issues after overclocking for N64/Shader usage. Tried the cheap heatsink route, and as suggested, did very little (as you say, probably the glue used). I've also tried larger cases with fans but the way it was set up meant it was just pushing warm air around, it was cooler but nowhere near the results I got with my passive-cooling case.

I looked into Flirc cases and then stumbled across the BIQU case, it's about half the price and works fantastically. I've never had the thermal symbol show since using it and the case itself doesn't get too hot either (you can feel it is warm when being used, but no shocks or being too hot to touch as some have suggested with passive-cooling style cases).

I also added a little thermal paste on the points of contact - it may not be necessary but I had some lying around so thought it wouldn't hurt.