If they were OEM Motorcraft platinums, they are good for 100k.

 

Just don't overtighten then strip the threads, fine line to walk but figure it calls for 16-20 NM or ft. lbs so 18 ft lbs, no more. That's probably a good reason for blow outs. In the factory, the threads have a coating of something light, so put a light coating of anti-sieze and that's it.

 

Don't over tighten the COP bushings, there suppose to be able to move on the bushing by hand.

 

Chaning the plugs really isnt hard at all. You dont need to remove the fuel rail, but a swivel helps.
My father helped me change the plugs on my truck and it took maybe 45 minutes to do. He works in the service department of a Ford dealer, so he knows these trucks way better than I do.
We used a special sparkplug socket that has a sparkplug boot inside of it and that makes it a lot easier to get the plug in. You cant even really see the sparkplugs, so starting them with your fingers is out of the question.
Just make sure that you let the truck sit overnight so that it has completely cooled and be carefull not to crossthread the plugs when you put them in and you should be fine.
I definetely would not pay a dealership $1200 to do the job.