We just got back last night and used the Entertain code at Dollar for a rental last week. The person at the desk was nice, but kept insisting that we needed more room and an intermediate wasn't big enough.
Finally, I convinced him that I wanted the intermediate and he gave me my paperwork. We went out to the lot, got the keys and went to the parking spot. In the spot was an Intrepid, which is a full size. The keys worked and we left with it. I looked at the paperwork later that night and it still said intermediate but they gave me a full size.
I think they are overbooking the intermediate cars, so if they are really pushing the upgrade (for $7/day) to a full size, stand your ground and insist on the intermediate. You may end up with a full size after all.