Well I have never auditioned for corps but I will give you my opinions on some the subjects you talk about.
On this I dont believe they shouldnt consider you a canditate, I mean some corps judge you differently, they want talent maybe thats already there while perhaps another corps wants the best potential they can find. The corps wouldnt know why they cut you so why should they automatically throw you out, thats very close minded on their part.
I believe once a corps has a well established and successful program the members start coming to them, the ones that already have all the talent, they want to be in the most successful drum corps. Its kind of weird though because it poses a disadvantage to corps like the Pioneers, yet there was a point in time where SCV, BD, Cavies where all at that point at one time. Location could have tons to do with it as well, like California has so many great musicians, and talent, as well as staff, and because they are there they go into SCV and BD, etc. May not be the situation for all successful drum corps, but it certainly plays a part with some of them.
Ok well it does help if there are alot of old people in anything that requires teamwork, because then you are familiar with people and may beable to work better with them. However the staff plays a good part as well, the Colts would need a fantastic show to get them to that top 6th placement, the same with Pioneers. Look at the Cascades this year. Of course I am going purely on what I have heard but in 2002 they made finals, then staff changes started to happen, and now they scored a 61.950. Everybody who I have seen a review from said it was their show design, the stuff that the performers cant control.