In a similar boat, and have decided between the screen quality, scrolling issue, 5ghz wifi issue, and wobbly power button to give in and return it.
Frustratingly I'm having the worst customer service with John Lewis (UK) I've experienced of late. They were obviously aware of the screen complaints as they quoted back to me using the 'jelly scrolling' terminology which I hadn't even mentioned. They refuse to accept a return on the basis of any defect, nor will they take it back under distance selling/contract regulations as it's been opened! How on earth is one to know there's an issue without having opened and used the item.
As it stands I'll have to physically go into one of their retail stores to (again) have the argument with staff later this week. Even more frustrating when you consider I was intending to instead buy an 11" Pro (£200 more!)
Is anyone else have issues trying to return their Mini, or able to report success in returning? I did mention to them that Apple themselves will take items back, no questions asked, within 14 days. Disappointing that John Lewis can't offer the same flexibility. Guess I won't be buying from JL in future if they can't match Apple.