No experience with plastic vanes, but as far as feathers go, in the instinctive shooting class taught by Fred Asbell and Ken Beck, they teach that the orientation of the arrow doesn't matter. They teach the students to nock the arrow without looking at it, as an aid to instinctive shooting and hunting. The feathers will fold in when the arrow is shot and won't affect the arrow flight. What does affect the arrow flight is if the quill, or the stiffer part of the feathers right next to the quill, contacts the bow. To avoid this, Ken Beck recommends trimming the fletches of one arrow down to maybe 1/8" and marking the edges with lipstick or something that will make a mark on the bow if there is any contact. If there is, then rotate the nock until there is no more contact with the quill and the bow.
I suppose if you were into extreme accuracy, you would probably want to orient all your arrows the same when you shot them, along with a bunch of other things we normally don't do in tuning a hunting bow. But for normal trad hunting ranges of up to 30 yards, and assuming an inch or so one way or the other is as good as a bullseye, I don't think it matters.