Well, after much thought over the last few days, I just preordered. This whole things sounds like a great deal, especially since the old model of subsidizing phones is now gone. My wife and I both have 6's and so one thing that I was worried about was, if I wait another cycle, how much value are we losing in our phones?
I researched and researched and it seemed like that with getting 2 iPhone 7's that with the AT&T trade in, we would only be paying about $9/mth extra out of pocket over the course of 24 months. Sure, that locks us in for another 24 months, but that isn't really a game changer for us. I still wanted to make sure I got the info from an actual person so I just went up to the local AT&T store and talked to someone. He confirmed what I had deduced (and even encouraged me to stay on my grandfathered unlimited data package!), and so I preordered a Rose Gold 7 for my wife and I'm going to upgrade to a Black 7+ to try out the better camera.
So all in all, it looks like our bill will go up about $13/mth which is miles better that what we would've had to pay with the AUP, even taking into account what we could've sold our current phones for to help defray the cost.