Being in the Planning industry, I agree with you that the OMB plays an important role. I have seen many applications refused, even though they complied with all applicable policy. The only way to resolve the matter was at the OMB. Board members have years and years of planning experience. Now, I have also seen projects that should not be approved.... approved. Again, they were appealed to the board, and based on the applicable policy the OMB refused the application. 

Many people should understand that even a OMB decision  can be appealed if an error in law was made.