It depends on the number of people in your party and where you're planning on staying. Sometimes
free dining outweighs the value of a room only discount, and sometimes it doesn't.
It is likely that the discounts for December will be released by mid-August, so hopefully you will know what you're looking at before you reach the 14 day upgrade limit on your regular tickets.
In general, you can look at both options and compare the "savings." An AP used to be good for a 40% savings during value season. Lately the savings haven't been quite as consistent. You can go here to see the historical discount time frames.
http://www.mousesavers.com/historicalwdwdiscounts.html#codechart
If you let me know your more specific party size and hotel preferences, then I can tell you close to what you will save with each option (with some room for error since Disney will likely increase prices for next year, and we have no way of predicting what discounts will be offered when).
As far as tickets go, you will save some money with an AP, assuming your trip next year is the corresponding week before your trip this year.
2 (one for this year's trip and one for next year's) - 7 day + PH = $685.86
1 - 4 day + PH = $317.37 for a total of $1003.23
With an AP ($552.74) you would save $450.49 per adult on the trip. (the savings will be a little smaller if you don't plan on hopping during any or all of your trips)