It is my opinion that the fear of hell and the appeal of heaven do not really have much of a direct effect on people who do not already believe it. The greatest effect is on the people who are already believe the religion.
Good point. But isn't it true that the very concept of heaven and hell forms the basis of christian evangelism - preaching the original sin that all mankind is doomed to suffer in hell because Adam and Eve ate the forbidden fruit but since God love mankind he sent his son Jesus to save them from this eternal damnation. Many people buy this story and they converted. To that extent I think it had direct effect on people who do not already believe in the religion.
In my opinion the effect on people who already believe the religion is another thing. Here it is used to reinforced their faith, to persuade them to get reborn (even the same person could get reborn many times). For this some evangelist preacher even used the recording of 'cries from hell in Siberia' by playing the audio loudly to the listeners.