I am driving a Vitz for the last three years(2004)
As far as the fuel consumption goes on Motor way it delivers 16km/L in city it does around 9.5 to 10.5. Howerver I happen to go to Rawalpindi via GT road and got almost 19km/L.
Now you have a 2006 with 1KR engine coupled to a CVT box.
As soon as you bought you should have gone to a good toyota dealership and got the complete tuning done, as you get the original parts there. Change the Plugs(2006 1KR plugs are damn expensive but thaey last 40K km easily) Airfilter(original) fuel filter(original) and get the brakes seviced. The odo on you car shows 35K but brother 90% of the odos on the JDMs are tampered so make sure you change the CVT fluid. As you mentioned that you added the ZIC ATF, I recomend that you get the ATF changed immediatly from a Toyota dealership coz the health of your CVT is under serious risk. Use the orignal Toyota CVT fluid. Yes the dealership prices blow holes in your pocket but trust me they know toyotas better than anyone else in Pakistan.
As far as the Oil goes, yes it does make a difference but not a big one. You may get a Kilometer extra out of the oil grade.
5W/20 is the most fuel saving Oil(Not ideal for our climate).
5W/30 is also good with saving fuel and so is 10W/30
But as we run our cars in extreme heat we have to have 5W/40, 10W/40 or a 20W/50.
i personally use Shell Helix Ultra which is 5W/40 Fully Synthetic.
As far as you qouted that you car is doing 8 to 9 km/L I think it should do around 9.5 to 10.5 a liter.
Just be sure that you use the right parts(Originals).
TC