I agree with you, the car should remain CNG free
1) I have an A/T on petrol, I don't know which city you are in but I bought this car in Karachi (May 2006) and after 6 months moved to Islamabad (Nov 2006). Overall I got a an average of 9.5 in Karachi and was getting a 10.3 in Islamabad. But now as 7th Ave is open I get around 11.2 km/L, because there is only one traffic light left in my commute. It means 105km in Rs.500 or 9 liters for 100 km (whichever way of expressing mileage you like most ) I use the A/C 50%-70% of the time.
Fuel saving tips are not to go more than 3500 RPM and put in "N"-neutral on red lights or when you are stopped.
2) If you intend to sell the car I would recommend not to swap meters. I got a digital RPM meter installed on the side. The only calibration required is how many cylinders you have, after market meters have different wires so you connect the appropriate one to the "point", in digital ones there is a setup which also allows you to setup your redline, etc.
3) You see the box in the middle of the front seats? Get one of those DEFINITELY. The steering is very soft (although not powered) so you can rest your left hand and get additional storage space It takes a couple of days to get used to hook the seatbelts and reaching the handbrake but thats not a big deal.
Also a warning: Cuore lets you shift out of "P"-parking gear when the brake is not pressed - be very very careful because "R" reverse is the first thing you'll hit. No new A/T car lets you do that, and most modern M/T cars outside Pakistan require you to press the clutch to start it. Oh that reminds me, you can only start the car in "P" or "N". For the shift button the manual has a diagram for when it is needed and when it is not, slightly different than vitz but does not matter, because you don't shift a lot anyways.