You can't go by "look". At 25k miles on a tune, it is definitely time to change spark plugs. The electrodes wear down and make it harder to fire the spark. Rounded electrodes bleed electric charge, while flat elctrodes build charge then suddenly spark. Combine that with increased boost, and it is even harder to fire that spark. Something about relative permittivity of the fuel/air mix in the cylinder, I dunno, I'm just talking out of my ass.
E92 335i/6MT Dinan Stage 3: intercooler, oil cooler, intake, flash, exhaust, LW dual-mass flywheel.
Vishnu PWM methanol custom trunk mount, Diffsonline 3-clutch Salisbury custom diff, Ohlins Road and Track coilovers, Vorshlag camber plates, much more...
E28 M5 w/ buncha stuff, R171 SLK350