If you’re an experienced print buyer then you know the work it takes to identify your production problems, define specifications, and solve production issues. Someone must do this work to deliver your projects. If you possess the expertise, time, and resources needed to define specs, select manufacturers, and manage your projects day-to-day, then you should do so. In your case a print broker probably would not add value to your projects.
On the other hand, if you are short the resources needed to devote to the buying process, then enlisting the services of a print broker would be a good call to save you money, prevent waste, and insure timely delivery of projects.