Ricey, send us a photo of how you get the coilpacks off the rear plugs and then remove the plugs without undoing the upper plenum, and I'll believe you, OK? Then again, if it involves playing with yourself while you do it, I bow to your superior knowledge!
Greenacc, the plugs actually didn't look too bad as far as heat and fouling goes. The biggest difference with the older style copper plugs is that the copper electrode is larger, flatter and soft, and erodes with time. Sparks like a really nice small, sharp electrode to hit, which is why exotic metal plugs work better. Their centre electrode is coated with a noble metal such as platinum or iridium, which self cleans, and doesn't erode with time. That's why they've got such a long service life. Copper electrode plugs deteriorate more quickly, as they have a larger flatter centre electrode, and when the sharp edge wears off, sparks can be a bit erratic and the gap increases as the electrode erodes. As for improvements, well, I've only just replaced the plugs so I can't vouch for any vast improvement, but the car is a little sharper on mid range response.
m1lky, the V6 quotes a 120,000 km interval for replacement of plugs. Pretty impressive, when you consider what they have to do over that 120,000 km.
Cheers,