They won't price match, I'm sure. And that is a big difference in price. But how many are flying? Are you the only one ? If so, it will cost you $25 out of pocket to fly SW. 2 people flying, it would cost you $225, so a little more than USAir. Are there other considerations, like airports, nonstop or convenient times that would be a factor? If SW comes out ahead with these, I would probably still spend the extra $25, if your credit is in danger of expiring before your next trip. If you have more than 2 people flying, the difference in price becomes more of an issue. Still, don't forget you can get another credit if your fares drop.
Which leads to your next question. Yes I do think your fares will probably drop. Early December is not a peak travel time, and they will probably have a decent sale. Should you wait? That's up to you and your risk tolerance level!
edited to add: I just looked at the website, and I assume you're flying out of either Albany or Buffalo? The fact that the flights are wide open is a good thing, and I would probably wait as long as those lowest fares don't start to become unavailable. On the other hand, it looks like prices are generally higher from either of these airports than some other markets, Islip Long Island (which is my airport) has flights available on those dates for $69. Good luck deciding.