Mick
As ive said before its called preventive maintenance. What you say is what we do very well in the bush here in aust. Your thoughts are correct. Trend trend and more trends. If you run the same aircraft it doesn't take long to make a plan. Trends don't just mean engines. It can be every component. If you have a fleet you can work out when they fail and make a plan around that. A failure dose not nessacilly mean before a component is due on an M/M schedule. If you build up your component record you can get extensions although a little harder these days.
Fine wire plugs generally used on lower cylinder's where oil and lead can cause a problems. A little of topic but I just change the plugs on my turbo falcon after 100000k nearly no wear. Champion place a resistor in there plugs for a reason. You will also get longer wear out of a fine wire as oppose to a massive electrode plug.
For the average GA aeroplane there really isn't much gain in either plug. However the more you fly obviously the greater the gain you can have. The thing I transfer to owners is fuel is the cheapest thing you can put into your aircraft.
One place I worked the 500hrly mag inspection was turned into an O/H this was due that the conditions that the aircraft was fly to get the reliability it was required to do.
At the end of the day it all comes down to costs and if you wont to do it.