Get your PPL. It doesn't help as much as many people think for the actual application, but it does a little.
I would say get it for the intangible reasons, because there it was immensely helpful.
You're going to understand concepts that other people will probably be scratching their heads at, especially early on. That may help in classes or other random parts of the Academy through your four years.
You'll gain some traits when you learn to fly that will help immensely at the Academy. This is the intangible stuff I was talking about. I still don't know how to really quantify it, but many of the things that help make someone a good (key word) pilot will also serve them very well in the Academy--if you are able to use knowledge learned in one area and apply it to a totally unrelated situation. Some people can't do that, so it didn't help them much. It also taught me to ALWAYS take the hard road if you have the option, it will serve you better later on. More on that at the end.
Doors will open if you have your PPL at the Academy that otherwise wouldn't. Of course there's the flying team. I was the last person cut for my year--it was my fault and non-flying/aviation related, darn those sub 3.0 grades. That was something I learned too late, other doors will close based on your GPA.
It helped me do much better in soaring, as well as make me a much more appealing candidate for being picked up for instructor upgrade--which by far was one of the best things I did there. Getting a chance to fly around every couple of days for three years, even more in the summer, for free--who can beat that?
Make sure you find a good instructor for your PPL though, that is much more important then how cheap the instructor is. Most people who had their PPL at the Academy, I wouldn't fly with them if my life depended on it (because it would). They sucked because their instructors didn't teach them much, only the min required, pushed them through at minimum time, and got the easiest flight evaluator they could find. Sure they may have had a more enjoyable time, didn't have to work as hard, and it cost less, but the end result was pretty clear.
My instructor worked under the philosophy that he would be the only person teaching me how to fly in my life, if he didn't teach it, or teach it well, he considered I would never get it later on, so the weight was on his shoulders. When he would teach me in the air, good enough wouldn’t cut it. If it wasn’t perfect, I would do it over again until it was. Furthermore, I would be the only person in the aircraft, there wouldn't be any one else to help me. It was up to me and only me to stay out of trouble, or if I did get in trouble, to be able to get out of it myself. If I didn't, I would be a smoking hole in the ground. He didn't want to see me on an accident report (I agreed with him). I had to prove to him on a daily basis that I knew my stuff and knew it enough to fly on my own in any situation. Because of that, he had a 100% PPL checkride pass rate with every student he had ever sent to an examiner (which of course I didn’t find out about until after the checkride).
I don't say that to brag. I say that to let you know the importance of flying with a good instructor. If your instructor isn't like that, go find another one who is. If you do that and take the hard road, what you learn will serve you extremely well, especially during your Academy years, flying later on, and throughout your life.