they're cheap enough, (relatively) and it isn't that hard to do. IF there is ANY question, I go ahead and change them. ALL of them. Though I WILL NOT pay $756, EVER, for a single spark plug change/ unless they come attached to brand new heads. NOBODY touches my truck but me. I paid about 10% of that amount, to buy all 16 plugs.
so, you have to screw 16 plugs in on one truck, vs only 8/// BIG DEAL!!! BOOO HOOO
Fords had the 8 spark plug 4 banger, way back in 1999. Unless you are somehow injured and/or handicapped, just do them yourself. I don't care what they say about "shouldn't be a problem" waiting the other 30k miles til they are "due" I would rather not chance it. It will cost you more in the long run if the threads are galled, or pull out with the plugs because you decided to wait.
I haven't gotten around to it yet (I have only had my truck 2 weeks) but for only around $300 I got plugs, wires, coil boots, a new belt tensioner a new belt, 4 oil filters, an air filter a cabin filter and I think a couple of other maintenance parts for it from Rock Auto delivered the other day. and I got the "good stuff". not the cheaper brands.