If the speedo is working correctly then the sensor is fine, but even without the VSS plugged in, it shouldn't affect performance in a negative way, it could actually speed the car up because you'd loose the torque restriction.
But if you are lacking power in low-mid RPM, that could be the cam sensor or the wiring too it. The signal is needed to make the VCT work, without it, you'll loose power low to mid range.
Lambda could also cause power loss but it would run very rich and lumpy/crappy all the time except maybe when you first run it and the engine is cold.