I'm looking for a basic rule of thumb to follow, as I'm only a mere Silver and have recently become aware of FlyerTalk:

My wife (also Silver) and I will be flying to West Palm on a 757 in December. Coach is almost totally booked, FC is totally open. Do I use miles to upgrade (As of Jan 1, it becomes 15,000, so I'm thinking I want to "take advantage" of this opportunity one last time, considering the mileage deduct upgrade is available), or do I hope for the automatic upgrade.

I know from previous experience, if coach is full on a 737-500, there is no chance of an upgrade for a Silver, and if you're on a 737-3,7, 8 or 9, a very small possibility of an upgrade, but I'm not sure about on a 757, with its 24 FC seats.

Also keep in mind that many people on the EWR-PBI route have homes in both areas, and are constantly flying back and forth (hence, a tono of Elite members). Any thoughts? Thanks.