There is one controversial, but ultra cheap, thing to try which is the opposite of dry feet and socks, as excellent as that suggestion is: vapor barrier.
I remember reading on BPL once that the biggest loss of loft problem with down bags was in the foot box area. So apparently our feet put out a pretty good amount of moisture. The cheap experiment can be done with bread bags or small cut to size trash bags. Probably more pleasant with the tinnest possible synthetic liner socks on your feet, but can be done with bare feet. Then roomy wool socks, or even down booties, over that. Or even nothing if your foot box is thick enough. I have seen this approach have impressive results, even inside boots while ice fishing. You never know, might work and costs almost nothing.
Your feet will feel (and be ) damp or wet. Which I find a bit unpleasant. But, look at it this way: that is moisture that will not be causing you any problems. It will not be evaporating ( nature's air conditioner called evaporative cooling will be 100% blocked). And any vapor that is being produced will not be condensing in your socks or foot box or booties. reducing loft/warmth. And any sweat also stays out of your insulation.
So for me, there has been a trade off: cold "dry" feet(or whatever) vs wet(skin only) and warm, with bone dry insulation.
BTW, with your cold feet: what are you using as a TQ/bag? What kind of temp rating?
PS: Crawldaddy: OOPS, I didn't see your post #30, covering this subject! So, what you said!