Personally I'd have avoided all this grief and hassle (it was totally inevitable tbh) and just have accepted the offer of the new car straight away. Life's too short.
I still would have to go through all this because I'd be keeping this car until the new one was built.
It's an absolute no brainer as far as I would be concerned. If your having so many problems you should accept the new car without hesitation. Would you not be getting the 7.5 for basically no cost and saving you a huge amount on depreciation.
The only thing I would be paying for is options, not including paint because I've already paid for it on my car and because I'd be going from 5 door to 3 door and the only option on my Mk7 is paint and sound and sport they will through in a DSG box or £1k of options.
It is not all about money though, as I've said before I can't get the facelift with either the colour I have or the sound and sport pack and I really like my car except for its faults which are getting sorted to a degree.