I'm another who fully believes diesel engines are NOT for the average person, those who aren't skilled or very experienced mechanics on those types engines. Having read a few threads here of the expense involved in "simple" repairs or maintenance scares the bejesus outta me.
Your V10 with 200K miles still has a lot of life left in it---on FTE there's one fleet operator who regularly puts 500K and more on his E-Series people haulers without anything more than scheduled fluid and filter changes. He has demonstrated the spark plugs themselves will last up to 300K miles without issues.
Repairing the blown plug shouldn't cost more than $400 per hole---should you go this route make sure the installer would use the Time-Sert brand of inserts. It seems those have a huge fan base of users and mechanics who've used them.
Here's two links to a huge database of information dedicated to the Ford Modular Motors, this first one for the V10 specifically:
https://www.ford-trucks.com/forums/forum49/
Within that same forum there's a thread about 5 Star Tunings whose owner Mike is pretty much a deity in the Ford V10 world, found here:
https://www.ford-trucks.com/forums/9...at-5-star.html. Along with his great product his dedication to customer satisfaction is simply amazing.
That's all just my $0.02 worth, take it for what its worth from a gas-only 5.4 owner.