I am a home inspector for Maple Trust Inspections in St. Catharines, Ontario.
I see appliances new and old every day. The electricity used when the fridge is running will be the same, however the electricity used over time to keep the fridge at a lower temperature will be less.
Lowering the temperature will save you money. So will keeping it away from heat sources, keeping the door closed as much as possible, keeping it full and even insulating it. Keep in mind that many areas have peak usage electrical billing and that using appliances such as the washer and dryer during off peak hours can result in big savings.