Depends on what you want to do. On a stock setup - there's not much point. OEM platinums are actually pretty good and long lasting.

If you are setting your car up for more performance - and have done other mods - then going colder on the plugs will help supplement what else you have already done. Which specific plugs you should go to - however depends on how much modding you already have.

As you know going too cold for any particular setup is just going to waste gas.