Resale price continues to drop. I recently saw an eBay auction for a gold plates 38 SS model for $550. Some sports models are as low as $250 on Craigslist.
Two things are happening. First, some people get them as gifts and they don't want them or they simply get tired of them. The second is that people who love them are selling so they can get a different color or version, especially now that gold sports are out.
The resale market is also limited as only a small percent of iPhone users want one at all. Those who really wanted it already bought it or will buy from Apple. It leaves few buyers in the resale market relative to how many people are looking for used iPhones and MacBooks.
So if you had to make a bet, I'd say a safe one is that the value will continue going down. Don't be surprised to see sub-$200 sports models and sub-$350 SS by New Years.