Paul - having just looked at that questionnaire out of interest, the other thing that strikes me is that the content seems to make the assumption that if you are attending the carols you are from the locality. It doesn't ask which part of the country you come from / why you are attending if you are not local etc - surely just as important a factor as the matter of why, if you are a local, you have dropped out ?
Last year I noticed articles in national press referring to the carols, and in recent years they have featured heavily in radio programmes etc,and that must affect attendance ... and possibly ,as a result, the drop out levels?