Originally Posted by RTIS250

Have you seen a cabin air filter at 30k miles? Gross.... you breath that air, its worth the money.

Spark plugs wear, its your choice to replace them or not. There doesnt have to be a rough idle to cause a degradation in fuel economy...

Transmission fluid at high miles thats never been changes, yes, it could actually do more harm than good. But at regular intervals, it is very beneficial.

Power steering is good to change every 60k or so. Fluid breaks down, sludges a little, and can cause leaks at seals.

Brake fluid, 2 years or 30k miles... the fluid is hygroscopic... it absorbs moisture. Its a good idea to change regularly..