Depends on the engine. Lots of engines out there on oem tune that are extremely easy on plugs. My old Subaru and Toyotas definitely were easy on plugs. Eco boost engines not so much. Coolant as long as its not contaminated ie watered down is an easy 100k item. Over servicing fluids is just wasteful and ultimately bad for the environment etc.
Anyone changing oil at 3000 miles today on anything other than a race car is just wasting money/ time and resources.
Caveat to that oil statement is, "and using a quality oil".
We aren't talking Subaru's and Toyotas. We are talking Ford Ecoboosts. Also, the Turbo charged Subies are not easy on plugs in general, so there is that.
Most Turbo motors are hard on plugs in general. When tuning it matters more, because of the gapping. As you know, that is one of the things that they lose or gain over time is gap. Changing them with a set of quality plugs WAY sooner than the recommended interval, has a big benefit on these motors. That is very well documented. it improves startup, idle, MPG, and general performance.