I know I'll get blasted for saying this, but I always thought that chemical warmers were a crutch. If you need them routinely are you prepared? Having them for an emergency is great but do you want to have to rely on them all day?
I don't mean to fly in the face of the libertarian recreationist in all of us...
I've seen zillions of those damn things not work when expected (too old, unlucky, whatever) and if you are counting on them for a trip in the woods without good footwear or handwear, you might just be SOL...
of course, some clever person will likely say, aren't those fancy mittens you wear a crutch? why can't you be tough enough to do the trip naked
now to the point: I often hike in the winter with my single leather boots and I realize when I wear them that I'm going to have cold feet but sometimes that isn't so bad on certain trips. Sometimes the extra comfort and flexibility (compared with my plastics) is worth the price. They are especially cold if they get a bit wet from sweat, which freezes, keeping your toes snuggled in with ice cubes!
I don't see any way around it other than getting warmer boots. Remember, fit is important too. If they boots are too tight and your circulation is compromised you'll get colder. Of course, all my boots are too tight so I don't really know the difference.
my three cents... fire away!
spencer