Keep in mind supply and demand. Its close to Christmas now so put an add in the paper that is a little higher than what you think its worth. People seem to always want to talk you down. It just makes them feel good.
The plastic parts and the shape that they are in will play an important role in the asking price. Is there duck tape on the seat? Are the tires slick?
Honda spree's seem to be a comodity right now. I've seen several in the local trader advertised for 300 or so and I cannot seem to find one to look at. They sell the same day the trader comes out. This would imply that the price should be a little higher than what they are selling them for. Look around your area. Like I said, availability is the key. If there are 15 for sale in your town, you might not get much. If you are the only player, you might be able to ask a little more than the Kelly Blue book. A lot of folks are wanting the newer scooters but don't have 1500 to 1600 to shell out at the dealer. Your type scooter is a good alternative. The Honda name helps too.
I personally wouldn't want to be knocking my knees with the handlebars but to each his own.