To check out your fuel filter just try to blow through it with your mouth. Almost any resistance is too much. Plugs are universal, same as your bike. Automotive wires usually sucumb to wearing against each other or really anything, the telltale signs are small white tracks or lines or spots an the wires where the spark is arcing out. Spray the ignition system with a fine mist of water and check for arcing or the motor dogging out. The only o2 sensor that affects performance to that degree is the upstream, or pre- cat one. It's purpose is mainly for air fuel metering, the down stream or post-cat is to measure the catalyst efficency. If taking off the filter cover does not help, look else where than the air filter, a little dirt will not kill it. Toyotas are BULLETPROOF i've personally seen many well beyond 200k miles. if the motor sounds good go for it. Best of luck.<( EDIT )> I wanted to add that if it is seeming like your O2 sensor try unpluging it, it should go into a default mode with no signal, and have somebody rev it up while you check exhaust flow, you could have a blockage or a kinked pipe.
