Installing a dedicated AC line

"His comment to me was that the 12ga better matches to the current being pulled across the circuit, smaller diameter, less resistance, less skin effect. I'm not clear on the explanation, I just remember he was quite clear in his opinion, and I trust his knowledge about audio and electronics."

Skin affect at 60Hz?

If you are willing to pay the extra money for 10 gauge wire, then go for it. You will have less voltage drop, less surge drop, and a more robust system. You need to make sure all of your circuitry, such as breakers and receptacles, support 10 gauge wire; as some do not and you DO want this to meet NEC.

Regardless of which gauge you use, make sure you use a good quality receptacle, such as a Hubbell. See http://www.hubbell.com/

Actually, if you are a real glutton for punishment, you can bring in 220 VAC and rewire your transformers in all of your equipment! This quadruples the efficiency and halves the surge currents.

Oh, I forgot to mention, put in a dedicated earth ground for your system. I have done this several times in several homes and it has always helped reduce EMI interference and made a whopping difference in FM reception. That being said, I wouldn't do the work for the sonic improvement, but it sure is worth it for FM.

I didn't think about this when I first installed it, but FM, as with all broadcast, is transmitted with respect to the earth, so a solid earth ground really cleans up reception.