I would replace your spark plug wires at the very least, especially since you had just replaced the plugs, just because its part of a tune up, and your mileage is high enough to where replacement isn't out of the ordinary.
The P0300 is a general misfire code, and as you have already stated can be a result of numerous things. Coils, wires, plugs, injectors, sensors, mechanical issues etc. Being that you are throwing a P0316 in conjunction with the P0300, I would think that they are related, but rather than throw money at the vehicle, do a few things first.
Replace your plug wires, chances are they are at, or close to the end of their life as it is. Check the connector going to the CPS for corrosion or a poor connection, clear the codes at advance auto, or autozone and see if the P0300 and P0316 codes come back. In the event that the codes do come back, or just one of them, you can rule out the possibility of the plugs and wires and move on to more possibilities. If the scan tool at whatever parts store you go to has the ability to monitor misfires, this could be a helpful tool to identify which cylinder(s) the misfire(s) is/are isolated to. I don't know if the scan tools they use have this function, as I have never inquired about it. In the event the spark plug wires don't fix your issue, and it is isolated to a specific cylinder, or group of cylinders it could tell you where to look next.
Good luck, and I hope you resolve your issue!
Last edited by Mattb2e; 07-14-2012 at 01:42 AM.