There are certainly a couple of benefits to Kaplan... (1) it offers structure to your studying if you don't have the discipline. (2) resources such as subject tests and practice exams available to you can be very helpful.
That being said, if you can budget your time and stay disciplined, it might be best to go with the blue book and purchase both top score and achiever for practice. If I had it to do all over, I wouldn't have spent the money on it.
Kaplan is probably worth more like $600...not $1300.
My two cents. Good luck.