i've mentioned before about the extra set of spark plugs. i think it's overhyped liao. many just hearsay and pass it on without really calculating and see for themselves. if your mileage is typical about 20 to 25k a year, you'll only need to change once if you are on normal copper plugs. if you are on iridiums, then you can stretch up to at least 3yrs before changing. so that will be like $20 for the extra set of copper plugs a year, or $60 for the extra set of iridiums over 3yrs, which works out to be the same.
now let's see the petrol savings, taking 25,000km a year and ron95 petrol.
15km/l = 1667 litres
14km/l = 1785 litres
13km/l = 1923 litres
average petrol cost after 5% station discount and credit card say give another 5% = $1.86
difference between 15 and 14 is 118 litres = $219 savings.
difference between 15 and 13 is 256 litres = $476 savings.
difference between 14 and 13 is 138 litres = $256 savings.
so with the same driving style, if you can achieve 15km/l for idsi and only 13 for a ivtec, then your savings is quite a substantial half a k. even if it's 14 vs 13, it's still a $256 savings in a year.
what is that $20 for that extra set of sparks?
regarding built quality.. i think fit/jazz still has an edge over city. eg, just press press on the door panel and you'll know