Well, here goes my jump into the action.
My comments are not official, but are based upon discussions with EliteLine folks, gate people and WorldClubs personnel.
I think the most important factors are:
1-Elite status
2-$ paid for your ticket
3-Date of purchase - the earlier the better
4-When you show up & ask to be put on the waiting list.

I know that there have been instances when I've been denied an advance upgrade, have gone to the gate & been told there are 10 people already on the list for 4 1class seats, and guess what - my Gold status puts me at the top of the list, obviously ahead of Silvers who are seeking day of flite upgrade.

Also, when going coach standby, my Gold status seems to put me at the top of the standby list, even if 10 others are already there first.

As best as I can tell on NWA only Platinums seem to go ahead of us Golds.