if you're n/a oem plugs are best. i believe the interval to change them is 100k miles. or 160k kms. depending on how bad the plugs are you probably wont feel any performance increase. tuning is not required unless you change your exhaust and intake. the ecu will adjust itself. if you are already tuned and your old plugs are real bad you may want to have the tune looked at.
Agree, no more power. Use NGK or Denso.Nice low mileage!!
really they should be changed whenever you feel the car is running strange or just down on power. You can always pull them out to check the diode and make sure they aren’t cracked or anything out of the ordinary. I changed mine at about 95k miles to an iridium plug and the engine sounded healthier, no increase to power though.