Don't know what your current mileage is, but as others have said, I'd change them well before 100k miles. From research I've done, I'll be treating my new DI 3.5 EB a lot different than I treated all my previous PI engine trucks. Carbon buildup on intake valves may not end up being an issue for you, but all DI engines are prone to that. Having a look at the plugs early is one indicator, and if done properly cannot hurt and may well help.