Im also looking to sell my 07 Pony Pkg with the Interior Up-Grade Pkg and the Preformance Pkg. It has 12K and is in showroom condition. I was hoping for $15K for mine, $13K for yours might be a little high.
In the future sometime I'll probably buy a used 5.0 with low miles, one that I can drive and not worry about getting a chip in the paint on it. I love my stang too and I'll probably cry when it goes after all the time I spent keeping it looking new. Im gonna lose my A$$ on it and that's the way it goes, I'll never buy a new car again, you lose too much money.
Buy that 5.0 and dont look back. Appearance mods and preformance mods wont get you anymore money, people like to do their own modding. As for the new paint job, that might actually hurt the price, it's not original and a repainted car raises questions.
Good Luck on your sale and hope you get what you want.