I did DCA-BOS-DCA Mon-Thurs for two years straight. JetBlue didn't have the schedule to compete. I was EXP, so was generally upgraded every flight, but not all. I don't know about the other direction, but I would think it might be more difficult as more people would be coming to DC for the week than leaving (just a hunch on my part). The Shuttle was rarely delayed or canceled and with flights every hour it was easy to change if needed. I did see PLTs upgraded fairly regularly, including on the 319s, but even not in F the flight is barely an hour and Y on the Shuttle gets free beer/wine so it's not the end of the world.