Dealerships in my made up math rule of thumb will offer you 10% less than you want and sell it for 10% more than you want.
i.e. $20k is reasonable private party value, they'll offer $18k and sell it for $22k.
You're going to get more money private party but you'll have to deal with the sellers yourself and there's the question of how the financing plays into it, technically you don't own the car, the financing company does.
http://www.bankrate.com/finance/auto...n.aspx#slide=1
Agreed with everyone else, if you trade it in put it back to OEM and sell the aftermarket parts on the forum.
Edit: I wouldn't bother with craigslist, I'd just use this forum. Looks like you should speak to your loan company and find out how they like to handle the transaction.