I take plenty of pride... I wouldn't be able to open my own business if I didn't. I am not arguing that it is better to rewire each speaker, but it is typically not worth the hassle and added cost for the slight difference you will see / hear. And by competition I am talking SQL not SPL.
IF the factory wiring is only 20awg (most is usually 18awg) then there is a .08ohm resistance per foot. At a 12 foot length, that's a power loss of 7.5w. Rewiring the system with a 16awg speaker wire (.04ohm / foot resistance) would give you a power loss of 3.8w. So in the end you are realistically only losing about .5db by using the factory wiring (assuming it is in decent condition without heavy corrosion anywhere). The average human ear will not hear a .5db difference.
Here is a nice little calculator that I've used before. You can enter in all of the information (power output, speaker impedance, wire size) and it will give you everything including the dB loss. http://www.bcae1.com/images/swfs/spe...rassistant.swf
The only possible issue is that if it is only 20awg then it won't meet the 300 circular mills per amp of electrical current standard... but it just barely doesn't meet it so there really isn't anything major. Plus, most factory speaker wires are 18awg (not sure exactly what Subaru uses).