I'd like to know what people really mean when they say "starting too early hurt me on the LSAT." I suspect it's just a cop-out. One didn't do as well as one would've liked, so he/she blames it on "studying too much".
Doing more practice for this test can only help you. There is no reason not to start studying now for next year's test. The earlier you get familiar with it, the better. I wish I had started studying last year sometime and feel it would have given me an edge.
Of course, it depends on the individual. Some people can score 180s cold - or after studying only a couple weeks - and others need a lot of time to absorb the techniques. But I feel, honestly, that the "stuying too much" notion is mostly myth.
The only thing I WOULD caution against is using up all of the practice tests - you'll want to preserve some untouched material to work through during the weeks leading up to the test. But other than that... study away! You'll be glad you got a head start on it.