Dude you can study all you want to... and studying isn't going to hurt, but consider this.
The ASTB is an aptitude test, it is not a knowledge test. So the benefit from studying gets your brain working in the areas of the test, but studying for a year is not going to drastically increase your scores.
Overall its a well designed test and achieves its goals. They dont WANT you to be able to study for the test, they want to find out what your natural aptitude is.
So what does that mean?
Study the gouge material out there, get familiar with the test format. Maybe play some flight sim games to get acquainted with the spacial questions, and then just take the test.
As for all the other stuff, I didnt even bother reading it because no one can tell you what you're chances are. I know guys who had a 3.2 who weren't selected for aviation, and I know guys who had high 2.x GPAs that did get picked for 1390 / 1370. It comes down to who you are competing against in your selection cycle, and more importantly THE NEEDS OF THE NAVY.
As to your experience with the Marines, it wouldn't surprise me. The Marine Air pipeline has plenty of people in it right now, and I know good guys who were attrited from primary for having far less trouble than I did.