The LSAT is by far the most important part of your application. Anyone that tells you it isn't is wrong. It was by far the weakest aspect of my package, and my admissions were highly predictable based on the LSAT score alone.
With that said, the LSAT prep courses are, in and of themselves, completely replicable. It all depends on what your motivation is. You have to realize that it's just someone one year ahead of you at the front of the room reading off of a script. Is that worth $1,000? Not if you have the diligence to take practice exams on the weekend. But if you're the kind of person who isn't going to be able to set 3 or 4 hours aside at least 5 to 10 times (and more if at all possible) between now and when you plan to take the test, then you should probably take the prep course since it should make you feel a little more obligated to do the prep work.
As the previous poster said, it's all about taking practice exams, though. If logic games are your weakness, get the
Logic Games Bible I found it amazingly helpful, as this was my weakest section.
And by the way, I'd have to disagree with what the last poster said about people not scoring as high as they did on the practice exams. It's all about taking them under REAL test conditions... set aside the full 3 hours and don't allow yourself any breaks that you wouldn't have in the real thing. My final LSAT score corresponded to the highest score that I got taking practice tests.
In the interest of full disclosure, I took the LSAT last June and got 164. I did about 7 practice tests in all, and I wish I had done twice as many.