a standard spark plug should last 10-20K KM...those better/performance type should last 30-50KM....
Spark plug is wear and tear part...
Also life span of spark plug depend on your engine condition...if your engine makan engine oil / wrong tuning then your spark plug will wear out faster.
I've oredi went to 6 shop at Jalan Pasar.. dont have those 12v L.E.D.. only 6v.. I want to replace all those lights on the dashboard with the super bright onee!!..