You basically cannot get hired at a major airline without a 4 year college degree.
Since you already have a 4 year college degree, you are fine. If I were you, I would get an MBA. You already have a bachelors level degree. The next step is a masters degree. I am pretty sure Delta is one of the airlines that has said higher level degrees increase your chances of getting hired. An MBA is a great choice.
There is nothing wrong with getting an associates degree in aviation (since you already have a 4 year college degree). However, it is really not necessary. A degree in aviation does not increase your chances of getting hired, anywhere. Getting an associates degree after you already have a bachelors degree is like getting a recreational pilots license after you already have a private pilots license? What's the point??
If you feel like getting more education (good for you), I would get an MBA. It is the most useful.