Unfortunately, there'* no quick and easy answer as far as a figure for your question. However, each (depending on how bad) except for the pcv valve, can significantly affect both fuel mileage, and performance.
The O2 sensor helps the computer decide the proper air/fuel mix and has to respond quickly enough for the information to be useful.
Spark plugs and wires - if each cylinder isn't firing properly, that means the fuel sent to that cylinder is wasted by not being burned, and does nothing to add to the power the engine makes.
If the intent of your question is to find out if it'* time for replacement, the short answer based on mileage alone is: O2 yes (ACDelco or Denso); plug wires - yes (NAPA Belden or other good quality wires - Taylor'* have been known to have a problem.); plugs - coming up on it. No Bosch or platinum plugs. PCV - pull it, shake it, see if it rattles. If it does - it'* likely ok.
Black 2000 SSEi, Silverstar Headlights, Angel Eyes fogs, 3rd brake light overlay, hi-flo cat, drilled 180 degree thermostat, Intense FWI, PCM, shift kit, and 3.4 Pulley. Solid front mount.