Spark Plug replacement on Lexus SC430, year 2002

[SC430ofOC]

I have the first year model that was produced (2002).  I have 122,000+ miles on it.  When should the spark plugs be replaced and how much should it cost?  Also, do you recommend cleaning injectors and thrusters; and, how much should that add to the total?  

[dcfish]

Your overdue, Yes, Clean all you can... Doesn't seem like you maintain the car well ???