£114 is a huge rip off: No way Nissan will be paying that, and tbh neither should they. Who's to say that it wasn't fine when you left the dealership, but the roads you've been driving on have been what's put anything out of alignment? Not saying that's the case, but tbh I think you're on a hiding to nothing if you chase that money back. They may well pay it, but there's no reason they should.
Caster isn't adjustable directly on most cars tbh, so it's not even worth worrying about. How does the car drive now you've had an alignment? That's what matters, not a set of numbers on a page. Don't get me wrong, caster can affect the steering, but it's not going to cause the problems you've mentioned. Dodgy at the front will, and now you've had that sorted...