The December fares vary greatly depending on when you fly. If you fly very close to Thanksgiving or Christmas you will find some fares are high. Thanksgiving is early this year, so that shouldn't have affected you too badly as your $156 fare shows. I'd probably lock in as the potential savings are less than $50 per ticket which isn't usually worth waiting to save.
The fares are also affected by when competition releases their fares. As JetBlue and SWA haven't opened up December 2005 sales, your $156 is pretty good. You can wait until April for JetBlue to open up December and a bit later for SWA to see where fares go if you want to see if something comes up. If you're really one to roll the dice, then wait until late August or early September when the fall fare sales are released and you can get $49 each way if you travel Tuesday to Thursday.
