I agree that studying helps, even if it does not appear to be working. The more you study the more familiar you are with the content, and that can only help.
I know looking at a range of scores can be discouraging… trust me … I know this all too well… but it gives me hope to know that I can score in that range and it makes me a little more confident than I would have been without taking so many practice tests. Sometimes I feel like I put all of this effort in and it rides on one day, but at least I know that I studied and gave it my all, as opposed to going in without any studying and trying to pull it off. (I know this does not work, I tried it… took the test on a whim… did ok, but not high enough to put me where I want to be).
So yes, I think studying helps, even if there is no definitive progress in that your score jumps the same amount every time you take it. God only knows I would love to see just a little bit of consistency in my scores.