do you have any intake fan? the most important part in a case is the fan in the front, which draws air (and dust) from the room into the case. An exhaust-fan is also fairly important, to get rid of the hot air. Also try to clear any cables that might obstruct the airflow from front to back. This is mucho importante.
The pic you posted was a graffix-adapter with a passive coolingsystem, and VERY few manufacturers use good solutions, so buying a new heatsink is recommended, no matter what.