My 2009 Avensis TR 2.0 petrol auto is due for it's annual/60000 service where it advises spark plug replacement. As the car has only done 37,000 is it worth spending £50 on a new set of plugs which are theoretically only about halfway through their life or shall I wait until the car reaches that mileage before changing them. My annual mileage is only 10,000s or so which would mean another 2 years before changing them. One piece of advice I've had is to have them changed on the grounds of age bu