I had my -P-school medical director explain this to me when I was in school... It still rings true, and I still follow his advice.
When you walk through the doors of the ED, it's going to take the better part of 20-30 minutes for the staff to perform any meaningful interventions on that patient (unless they are slow, and/or the patient is cramping or a trauma).
The ED needs to put your patient in the computer. Then the RN needs to triage them. Then they put the case in the "to be seen" by the doc pile... And the doc needs to get to it. Once the doc sees the patient, they order treatment (like, PO or IV steroids or pain meds) and then the RN needs to get the order, pull the meds, and administer them - that can all easily take over 30 minutes in a semi-busy ED.
So... If the choice is, sit in the ambulance bay for a minute before going in to push another dose of pain meds, or give steroids - we should do it. It's what is right for the patient, and will reduce their discomfort and suffering, and quite possibly lead to them getting better faster.