As a CO Gold or Silver, even when flying HP, I've had an agent come back to coach and escort me up to F before the door closed. That's never happened on NW.

As for connection upgrades... on HP... for awhile there earlier this year I was only CO Silver, flying IAH-PHX-SEA a lot, and found that the HP agent at IAH would regularly nail down my upgrade for PHX-SEA and hand me an F BP, even though we were still three or four hours from that flight's departure and the "list" could theoretically change a lot in that time, esp. with PHX being Misconnect City.