In March, they sent out pin code room-only discounts that covered part of December; we booked a 30% off room through the first week. The only discount I see now for December is AAA/CAA members discount. I think those usually run 5 - 15% off the room rates.
Definitely jump on it when you see the discounts come out because they only offer a certain number of rooms, and they seem to be having less trouble filling them in what used to be the slower time between Thanksgiving and Christmas. If you know for sure you will come discount or not, you could book your room only reservation to hold the space, and then watch for applicable discounts (this is what our TA does for us). Then call back and ask to have the discount applied. They may need to cancel one reservation to make the other, but at least you'll know you have a place to stay no matter what.
Another thought is to call Disney directly and ask if there are any pin codes attached to your address. Several members here have reported success with this tactic.
Nik & his favorite guy Goofy at DHS Osborne Lights
Sandra in Northern VA