I am sorry to contradict what 46Driver has to say but the particular job I am in right now does require an aviator/NFO type to be in it. There are a few of us who work in my office and we work on mostly aviation specific stuff. That being said, the vast majority of jobs do not require you to be a particular type of officer. There are many billets for "operators" like SWO's, Sub guys, infantry, armor, etc. and there are others that require Intel types (a lot of those around here) but there are few that require aviators specifically.
As an O-4, you will not have a direct impact on policy and plans usually. However, you might end up doing a lot of background, writing, or laying the groundwork for policy makers who will be making the big decisions. I was in a meeting the other day where we discussing some policy decisions. The group was to make the recommendations to a policy maker. They will do what they want but your decisions at he middle level will influence them, the degree of which depends on the situation and the person. So while you are not going to greatly influence policy, you might have a little impact on it, if you are lucky.
One more thing, your background as an "operator" is valuable, you would be suprised at how many people who are the decision makers do not have that kind of experience.