When I bought my previous campervan (v8 modular engine, so same family as V10), it had 95k on it. Oh hey thanks, now *I* get to do the scary spark plug change (recommended at 100k). Oh I was SO, SO nervous about it. As it turned out I took it to a one-mechanic shop in the middle of Montana (due to trailer issue), but it turned out to be the perfect chance to do my plugs. He was patient and conscientious. We blew out the plug wells the day before, then hit each one with Kroil (a getter-unstucker spray) just as good practice. Then of course half the engine was removed (or so it seemed

) and then he gently eased each plug out. No guarantees of course, but they did each come out with no problems, then he put the new ones in just as carefully.
I sold it a year-and-a-half later with 130k, and the next owner (a friend) sold it like three years later with something like 175k -- no problems with those plugs.
When I bought the Chinook it only had 49k on it, but I had the plugs done right away at a Ford dealer (was traveling, no good shop as in the above case). Not sure I would do it that way again, but at least so far (four years, 25k), no problems.
If/when I have an issue now, I think I'd choose to go to the mechanics in San Diego that specialize in the inserts. Just to have complete peace of mind (then I can worry about OTHER things

).
Scott: COP, that's it - thanks, now I don't have to sit bolt upright at 3 a.m. suddenly remembering it. And agreed doing the coils/boots (or at least investigating them) might not be a bad step.