Acewarlock-
While the engine may perform well with just a change of the spark plugs, The engine is well used, and has served its purpose for many years. Due to the advancement of technology though, the engine is no longer performing nearly as well as the newer engines. Yes, you could save your money and put the new plugs in your engine, but eventually, you are going to have upgrade that engine to regain the performance you think you once had. The newer engines are so much more efficiant, and are so much easier to work on.
Moral of the story, if you just keep replacing the plugs, technolgy is going to pass you by and leave you in the dust.
Have a wonderful day.