I'll tell you what someone told me before I took it:
If you have the discipline to study A LOT on your own then you don't need it. If you don't think you do, then take it. After all it is only your future right?
I'll say this. I wanted to improve a lot more... but my score went up 5pts as a result of kaplan. That was enough to put me in the next score band and had I not been in this band none of the schools I'm looking at would even give me the time of day. So, I guess, I suggest it.