Tricky question, the belt is rubber, rubber perishes over time, most cars replace at four years. Do you replace?? Entirely up to you, take a chance considering the low mileage you do and hope that it does not break and end up with a bill of probably £1t plus or have it changed, its a question that I have asked my self many times over the many years of being a low mileage driver and each time I have gone for a replacement. Lets see other answers , different preferences.