mate i work for a parts place.
The NGK platinums are supposed to give a better spark and last 100,000kms. My customers always freak at the price as well, so i give them an alternate standard NGK plug.
For Eg. Even the 100kw corolla motor specifies platinums.
(my old motor)
It specs BKR6EP plugs to be used, and i had no reason myself to use them so i used BKR6EY (has a "Y" grooved electrode rather than the Platinum one)
I prefer to pay $3 a plug and change them more often than pying $20 for the others and having to clean them all the time.
Basically just replace the P on the end with a Y in most cases