Many times in professional development cultures we get hooked on the idea that knowledge alone can solve a problem. Yet the problem that we are trying to solve might not need that degree of expertise- instead it might be more fruitful to talk to students, parents, janitors, staff etc. about what they are experiencing. Spending designated PD time to talk to or understand other stakeholder's points of view could help generate a deeper conversation and ideation period that could greatly enhance the understanding of the problem being studied and lead to more fruitful collaborative efforts that impact the current needs of the community. By broadening the scope of how we define a professional development "activity" and allowing greater flexibility might help drive engagement and value of the time.
Also- I think it is important to really think about whose knowledge the teacher's value. If departments, grade levels, or individuals want to have a chance to work together there should be a space/platform where they can work to their own goals for learning. This should be an open space with no set outcome from the start- let the learning be generated from the time together.