Hey Lilly,
That's an good question (and I'm glad to see you're considering all aspects of your application!). Were I in your position, I would probably wait a year to apply. Here's why:
1. You don't have that long before the December LSAT--just five weeks. Five weeks is not a lot of time to make a significant jump in scoring (I don't know what you scored or where you'd like to be scoring, but I'm assuming you'd like to go up more than 3-5 points; and five weeks is not a lot of time to go up more than five points, if that).
2. If you take the December exam, your results won't be available until January which, as you pointed out, would essentially void any significant advantage you could get from rolling admissions. Although all law schools still accept the results of the December LSAT, you want to get your completed applications in as early in the cycle as possible (September/October, or November at the latest) to really get that edge. After that, you'll be submitting with the bulk of other applicants.
Here's what I would probably do, were I in your shoes:
1. Take the test again next February or June (although I would probably choose June, simply because it is disclosed, and the February is not--that's a personal preference, though).
2. Spend the next few months studying to get my score where I want it.
3. Spend next summer working on my applications (even though the 2012 apps won't be out until next September/October, they rarely change significantly, so if you print off this year's, you'll be able to have a pretty solid idea of next year's).
4. Submit my apps with my new score as early in the 2012 cycle as possible.
5. Celebrate when I get in to my top choice school.
I hope that gives you some guidance! Please let me know if you have any further questions--I'm glad to help out further.
