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.
Guys..the auzzies have use the Apexi Power FC ecu in their Altezza and have kinda solved the low torque range issue that all altezza have. Go to this link and read about it...