From running a few competitions myself I now for certain that if it takes too long then people will not take part, higher rewards does compensate to a point, like in Alive Chat for example, and one other thing is to always mention the participants so they come back, and the fact is I will soon add a similar feature to Alive Chat that I do in This Is Awesome where we have winners with the most tickets too, and that tickets are rolling over.

!ALIVE