@Umair,
We have same model in MT, It gives us 11-12 in city with AC, Never tested on long routes. I just checked from honda classic, They said the mileage will get improve after 5000kms of drive.
No need to change plugs before 100,000kms, City comes with long life plugs as i heard. Correct me if i am wrong.
Edit: Sorry i repeated the same thing as Dr.Kazim did. I haven't seen his comment 