very neat ride, masha'allah.
I am not sure about the price of the plugs, but I can check. they cost a bit more than regular plugs, but they last longer and you don't have to regap them. but i dont think there'd be a noticeable difference in performance
caltex havoline formula is 10w30 i guess, which is good for vitz.
do share your experience of pick and fuel average after removing the cat