I sympathize with my friend's situation. And it could be that the problem is intractable. But my advice was that his unit develop a mission statement (or locate, revive and revise one that might already exist).
Mission statements are easy to mock. I can't help but think of Jerry Maguire's earnest attempt to change his business with one. But my experience is that when taken seriously and disseminated widely, they're very helpful in just the sort of situation my friend is experiencing.
His unit has some sense of who they are and what they do, but it's not explicit and it's not shared. That leaves all its clients and constituencies free to define the unit's identities and functions to suit themselves.
A mission statement is the first step toward differentiating between the good things that it would be nice if somebody did, and the good things that are your particular job. If carried through as a guide to planning, it tells you what you should spend scarce resources on -- money, employee time, energy and effort. It outlines a core set of responsibilities. And it helps other people understand where you're coming from when you make a case for how you do your job (not to mention a case for particular resources).
You may think you know all these things without having to write them down. But does everyone know them the same way? Does everyone agree on them in principle? How many conflicts arise because people disagree on the very notions a mission statement makes clear -- what goods are to be pursued and in what priority, who is to be served?