We are a group of 10 touring Spain in early September and I was wondering whether we should just take the bus between cities which is very reasonable or whether there is anything worth seeing between these cities that would make it worthwhile renting cars or hiring drivers to allow us to stop along the way. Our tour operator suggests the bus as the best and least expensive way to go.
You could swing by Arcos de la Frontera. It's not on the direct route though.
http://www.spain.info/en/que-quieres/ciudades-pueblos/otros-destinos/arcos_de_la_frontera.html