First of all let me say that I own a 73 Challenger and love the 72-74cars. That said, 72-74 cars are a tougher sell. They aren't sought after like the 70-71's. That's part of the problem. Is the car priced too high? If it doesn't sell then it's priced too high. If you want to sit on it for a long time, someone might come along who will pay what you are asking. If you need it gone, then you'll need to think about lowering the price.
I think you would have an easier time selling a car that was in worse shape. Your car looks really nice but for $17,000 the buyer will have to be someone who wants to drive it as is. If someone is looking for a project, they will buy something in worse shape that they won't be afraid of modifying. It takes a lot of money to restore one of these cars. It makes it hard when you have to spend a lot on the car to begin with. People do it all the time with the 70-71's but not so much with the 72-74's.