Very sensible and always worth doing if there is doubt they have been changed for a while.
Its remarkable (ok, lets actually say it's bloody stupid) that owners of petrol driven cars fail to change the spark plugs at regular intervals. My first TF ran quite poorly at first but a change of plugs transformed it into a little great runner with less than an hour's work.
A friend recently bought a tiny Toyota IQ, a very small car with a very small 3 cylinder engine but tall gearing. It had no grunt at all in the lower gears and I couldnt believe it was made to run like that. A change of spark plugs and air filter immediately changed it back into the nippy runabout it was designed to be. Now i can understand someone shying away from a plug change on a V12 Jaguar or something exotic that needs half the engine dismantled to get to the plugs but it beats me anyone sane would put up with crap performance on straightforward cars for the sake of less than an hour's work with basic tools.