A small proportion of people do vote on the basis of who they think has been hardest working. And there are a significant proportion who complain that we “only ever come during elections” (which is not true).
However, keeping in touch with the electorate is a key part of being a councillor (or any elected representative) and doing that through a political party a way of doing that. The leaflets reflect, to a degree, the manifestos of the parties and give an indication of the work that the candidates have been doing. They are not spam.