There's a lot of variables that only you can decide.
1. Is your current degree worth a crap? I say that, because some people go to college, don't know what they want to do or be, and get a general education in the liberal art degrees. Fine I guess if it's a degree in math or science, but if it's in theater arts or similar, then what are you going to do with the degree. If it's a degree in something you want to have a career in, then that's fine.
2. If you go to the academy, you will start all over. Yes, you'll be able to bypass/test out of some pre-req type classes. You could even have enough time to double major if you want. Or if you take the classes at the academy and some are what you needed for your senior year at the previous school, you can even transfer academy credits to your first school and graduate with 2 Bachelor degrees.
3. Here's the big question. How old are you? When you say "After my junior year in college", I assume you are a sophomore now. And you're assuming you receive an appointment next spring at the end of your 3rd year. The reason I ask your age, is because if you turn 23 years old prior to June 2013 (The day you go to basic training at the academy), then you are too old. But chances are, you'll be 21-22 years. So age should be OK. Realize however that you'll basically have 1 shot at this.
4. Finally; the academy is not; or rather "Should Not"; be a goal. It's only 4 years. If your goal is to serve in the air force and serve your country, then the academy is one way of getting there. So is ROTC and OCS.
I know of student who have gone to the academy with a completed B.A. degree. They are very happy with their decision. There are some that simply don't want to go through all that schooling again, especially with 17-18 year olds. Only you can decide if it's right for you. Best of luck.