Your idea of overbooking is based in some form of Georgie Reality that doesn't exist. Simple math solves your equation......... there are always 8 area qualifiers with 8 guaranteed spots leaving possibly 64 riders at any regional in any class. They are trying to have full gates in all classes at the regional but you never know who will get hurt, not have the money, have bike problems, etc etc between area and regional so they give more "spots" than gates out hoping that a full gate shows up. When run properly (like Red Bud does), regionals with qualifiers are great so that 2 of your 3 motos are full gates with one qualifier moto that does not as it's split in half.
And if you are running outside of the top 20 in your half class for the first moto and have to go to the consi...... chances are that you aren't a Loretta Lynn's caliber rider anyway and this was just a pipe dream to make it there anyway. There are plenty of riders at the regional that "have no business being out there" in any of the classes.