The folks who have suggested that you remove accessories and sell them separately (ebay works well in my experience) are on the right track. You never get your money out of accessories, and if you include them in the trade, you really get reamed. However, you can usually recover at least half the cost of accessories when they're removed from the bike and sold separately. There's one disclaimer though .... if the bike you have the accessories for is not a popular model, then you may have trouble moving the accessories too. There's got to be a market for what you're trying to sell, and fortunately for you, there are a lot of H-D's out there.
As for the value of Harleys on the used market, it looked to me that the value was established during the period when H-D was trying to ramp up production. When there was a shortage, and people were waiting a year for a new bike, then the used bikes had great value. Once H-D was able to meet the demand for the new motorcycles, the used bike values fell. The other factor in play is that the baby boomers are, for the most part, now finished with their mid life crises, and those were the folks who were buying. The ones who are still riding, have moved on to other marques. Lots of low mileage Harleys are still sitting in aging owners' garages, and they'll be sold when the owner dies, or needs more space.