Re: X-PLAN success stories? 2013 GT
^^ This. What I would do is try to negotiate the best price before letting the dealer know that you have an Xplan number, and then once you've hit rock bottom in the negotiation, ask to see the Xplan price.
The Xplan price is a set price and the dealer is bound to include all applicable incentives available at the time of purchase, so comparing the fully incented Xplan price to your best negotiated price is a smart way to go.
If the Xplan price is better, then it's "Oh by the way, I have an Xplan number and I'll buy it for that price."