I traded a EG classic in July 07 on my copper top SG, only got 11,500. I also have a 05' FatBoy with a ton of extras bought Aug. 04'...8,200 miles. SG 8,000 miles but the FB is alot more fun in town and at Daytona. If you can swing it, keep the FXDB. Everyone needs 2 bikes.
I'm probably the prime example of what you're talking about! I just traded in an 08 crossbones in denim black, with windshield, rear seat, and sissy bar for an 09 Electra glide standard. The dealer gave me 15,200 for the crossbones with 1800 miles. I figured since the 09s just came out I could get probably 16,500 or maybe little more or little less. But I am very impatient, and when I want something I get it! Besides you only live once!! Plus I really, really, really, really LOVE the Electra glide!!!!
Sounds like a big hit, I'd sell it privately and buy the bike you like. You won't ride two, at least not enought to justify keeping it, and besides you will lose more when you decide to sell it later.