You could bind the reRender to some bean property which hold's id's for reRender. It should return "" when no changes found. It will be more optimal because in that case content will not be rendered and passed to client.
B.t.w. maybe push will be more suitable? Check livedemo sample with the dataTable.
Thanks. That seems to be working. For clarification though; I always need to rerender the area that contains the a4j:poll tag otherwise the reRender bean property would not be available, correct?