Over on his blog, Nobu an RTL-SDR experimenter has made a post about cooling RTL-SDR dongles (post is in Japanese use Google translate if needed). Nobu writes that another RTL-SDR experimenter, Toshi, has previously pointed out that an increase in heat appears to reduce the sensitivity of the RTL-SDR.
From his measurements, Nobu found that the internal temperature of the RTL-SDR can reach up to 70 degrees Celsius. So in order to cool the RTL-SDR Nobu has tried two methods. One involving using small cooling fans, and the other involving adding heat sinks to all heat producing components. It seems from the translation that he writes that the improved heat dissipation has extended his ADS-B reception slightly.
If you are interested, Nobu also has a previous post where he also mentions cooling of the RTL-SDR.