Complete burning of the fuel-air mixture hasn't been a problem on any car made in the last decade. Thank environmental requirements for making OEM ignitions have a plenty hot enough spark. This is a case of good enough being good enough.

You can bet the S wouldn't have a ULEV rating if it couldn't fully and reliably burn the charge, every time, with the stock plugs.

 

LEV is all about what comes out of the tailpipe not the exhaust port. The stock plugs make some compromises to last 105K miles. You can bet on anything you would like but after trying the options I am no longer using the platinum plugs.

 

Couldn't feel a noticeable difference at all. But then again, I'm not biased cause I got mine for free.

 

The main reason for indexing is so that you can see which way the ground electrode is pointing.

 

You don't use a torque wrench, do you? I would expect a half turn would easily double the torque (or more).