It really helps. Aside from flaps extension, you would have alternate braking with anti skid, waaay better than relying on 1000 PSI. Even if the priority valves prevent you from extending the flaps due to the hydraulic demand to the flight controls system, I believe its worth a shot. Worst case scenario you will remain in a dual hydraulic failure you already had in the fist place. Why waive such valuable resources in order to protect a system you had already lost? As Earl mentioned its probably not part of the procedure because the YEP depends of GO IF items, but they could’ve added a note mentioning it as a possibility on the FCTM.