If you want to see the more out of the way resorts (AKL comes to mind), I'd say drive over there. But for the MK area resorts, my plan would be bus to MK -> boat to WL -> boat to Contemporary -> monorail around to the Poly and GF. For the Boardwalk resorts, I'd go on a day you were already at Epcot (since the walk from the bus/monorail to International Gateway is quite a haul), or at MGM, and then it's pretty easy to walk around Crescent Lake and hit all those resorts.
One other tip - and more of a 'my opinion' thing - I'd skip the moderate and value resorts unless you're really bent on checking them all off. Since they're spread out between different buildings, the decorations tend to be kinda sparse.
One other thing, not related to your question directly but something we experienced last year!

'Holiday pricing' comes into effect for certain restaurants, mostly the buffets, the week before Christmas. Last year we were there the 12th to the 18th, and the price of the same buffet breakfast was about $5 more per person on the morning of the 17th than on the morning of the 13th. Our server explained it was the 'holiday pricing' kicking in. I'd never been at WDW close enough to Christmas for that to be a factor before (apparently they've been expanding it in recent years too). Anyway, something to be aware of.
Crowds-wise it was full-ish but not crowded. I think the only waits we saw consistently longer than an hour were Peter Pan, Soarin' and Test Track, and I'm pretty sure the waits there are longer than an hour even when the parks are closed.
