Cory,
I understand your reasoning, but I think it should still be a straight vote for a couple of reasons.
1. Only 3 of this years entries were in the calendar last year. Because there are more than 13 other entries there wouldn't be a remainder of last years entries to vote on. They would just be automatically discarded, which I don't think is fair.
2. I think the calendar should showcase the best photos possible.
If a majority of the entries were repeats from last year I would see a reason to maybe mix it up a bit. But I don't think 3 is too many.