Very nice, thanks for sharing ur experience.u are certainly right about the mileage issues of lahore/karachi honda city owners.we cannot blame it on the car at all.and ur car is still @ 4300kms so the figures will certainly improve and if u learn to drive economically (which i believe u already have) u ll touch 20km/ltr anytime when 10,000kms mark is crossed.
For 5000kms inspection, honestly, its just a marketing gimmick, they dont really INSPECT the car properly.they just lift it up, tighten some nuts and bolts from underneath (which are most of the times not loose even a bit) they ll check the oil and water level in the relevant containers and off u go!
theres no need to get the diagnostics performed at 5000kms or any mileage unless there is a problem or the check engine shows up. mileage will not increase by getting ECU diagnosed. so i would say just wait for 10,000kms.
oh, get the engine oil changed at 5000kms if u havent done that already.