Have you called YOUR insurance and see what they can do? Seriously, if your car isn't right, they should do everything they can to make it right. If you love the car, fight for it.
And FWIW....I AM old....so driving a C5 doesn't jive me.
Its hard to tell from those pics...but is it possible the body panels are right and the brackets for the taillight are the things that are out of alignment?
It would probably be worth getting a second opinion, an estimate from a reputable shop that sees what you are talking about. That way, you have it in writing that A) the car is still not right, and B) how much to fix it.
Just so that you guys have some idea what kind of crop I'm dealing with here
You mean crap!...a crop is what you harvest once grown
And yes I'd fight that bodyshop for a shoddy job. Not acceptable! And as far as trading it in, you'll still get zonked if they do a carfax or a decent enough inspection. So it's not like you're going to dodge the bullet unless you're dishonest to the purchaser. Might as well get it fixed right, then consider if you really want to sell.