It will be interesting to see the responses to this thread as this is, IMHO, one of the great mysteries of the airline business.

In my experience, if you don't have a reservation on a flight, elite status won't help much in getting priority on the waitlist. Bumped or delayed pax from other flights and full-fare customers seem to get on the plane first. On the other hand, if you DO have a reservation on a flight, elite status seems to be the most important thing when it comes to FC upgrades.