My wife and I got new iPads for Christmas this year. Both of them have a bit of dust under the screen. I had to go looking for it to find it. Even with my glasses on, the only way I can see it is with a flashlight. It is not even a little bit visible while in use. Seeing as neither of them has weird tints and very minimal book spine, there is no way that I am jumping on the exchange roller coaster with these. After all of my iPad 3 exchanges, I learned that I need to pick my battles with these things. I don't like my odds of getting a flaw free one on exchange.
Great decision. If I would see something like that doesn't interfere with my usage, I don't think twice about it. And I'm speaking about electronics in general.
Time is money.