I'm having my 2006 honda city 1.3 cvt serviced for 20,000km. it's time to replace the stock spark plugs. Honda quoted an estimate of 7k (Honda Synthetic oil/regular spark plug) and 8.5k (Honda Synthetic oil/Iridium spark plug).

Question:
(1) is the supposed benefits in using Iridium spark plugs worth the 1.5k price difference? Honda sched for replacing spark plugs is every 20,000 km.
(2) primary benefit that i'm looking for is Fuel Economy (currently mine is ~13km/l), can iridium sp still increase this?

thanks in advance!