Not a bad idea IMO. The crucial factor of all of these decisions is "how much data do you currently use and how much do you forsee yourself using in the future?".
The other thing to consider is that when it comes time to upgrade devices, you will be buying them outright rather than having them subsidized. So while you may be paying $5 more per month for the "gotcha" plan, it will really be costing you much more if you ever intend to upgrade your devices.
I don't understand your second paragraph. Has AT&T said that they will not offer subsidized phones under these new plans? That would be a problem for me, as I (and my daughter) have "upgradeitis".