Just my two cents, because I have not gone through due process, but I've read through a lot of cases where the same 3 or 4 advocates testified and the judges apparently knew them well.
People like Rich Weinfeld are essentially hired guns to guide you through IEP development and implementation. While they often participate in due process, I think their reputation as hired guns makes their testimony less credible because the judges know they will say whatever will help their client.
If I ever did go through due process, unless it was a slam dunk case, I'd probably use someone who does little or no advocacy and is more involved in testing and educational program planning. Along with a good lawyer, of course.