My advice is don't waste money on such expensive plugs, if you insist on spending such amount, spend on top quality fully synthetic lube oil.
I've maintained my standard plugs from day 1 and never changed them yet, my mileage stands at 21k+, I last cleaned and regapped them at 17k km.
I've not felt power loss, heavier consumption or whatever issues. I'll probably replaced them at 30k km at a fraction of iridium price.

Me will rebuke these claims with 1-2 major reasons by experience. Maybe I could believe it could be worth for fit and forget it till you sell of the car after 5 years...
http://www.ngk-sparkplugs.jp/english/techi...01_1/index.html
Only when your plugs are very old and haven't been serviced/regapped during service intervals. Re-gaping and maintain sharp edge can prolong the service life of the plug till time to change. It one of the easiest job to do this. And how much is one set of these OEM plugs? RM40 at your nearest friendly parts store?
Also at RM180, you can buy top quality synt lube, Branded Dot 4 brake fluid, and Toyota Long Life coolant, all have to be changed periodically for best performance and reliability of your car.

One thing IMHO, I don't believe service centers will be consistently top quality (yes, they may do and having better adherence to manufacturer SOP) but they're also vulnerable to staff turnover and different mechanics or reception staff, save routine service of lube change and minor services. Different mechanics may have different attitudes and may differ in skills. But for self assurance, I feel more confident with authorised service centers (not always price issue) and they're likely easier to deal with with some warranty of repairs undertaken by them. I don't like argueing with other 3rd party unethical shops. Hate them washing their hands by saying..Liedat wan!..Hai Kum ke yong mah!....LOL!

This post has been edited by bsl555: Nov 21 2015, 05:35 PM