I just changed the plugs in my 2004 Superduty at 145,000. I developed a miss too, but it was a carbon trace through the boot. Still runs a hell of a lot better with the new plugs. I had a 13 year Ford tech help me out (friend of a friend) because of the blow-out issue I wanted to make sure it was done right.
He did mention in conversation that a GOOD tech can get the two piece plugs out of the 3 valve modular engines without breaking them. They get the motor very hot, and then use an impact wrench on a low torque setting. This has been discussed on some of the flat rate tech forums as well. Fuck a $3k plug change. He said the shop he worked at just added 1/2hr to the book time for plugs and called it a day, if none broke you got some extra time. If they all broke you lost, but that was rare.
As for power adders... There's a supercharger kit for it that adds about 100hp. That's about it. All of the easy stuff, tuner, intake, cat-back, etc, only adds 5-10hp. Not worth it.
My power steering pump is dying. My alternator went out a year or so ago. Other than that, my truck has treated me real well. Valve covers are leaking, so I'll need to do gaskets on them sooner or later.
-Jay