I've been watching and comparing data plans from VZW and ATT for years, and in the recent few months, I have never seen so many price changes (mostly lower) from these two providers since T-Mo started rattling their cages. VZW made the latest move where they start the $25 per line discount at 6 GB ($70) on their More Everything Plan, vs ATT, where the $25 per line discount doesn't start until the 10 GB ($100) Next plan. I don't think it will be long before ATT again shuffles the plans to more closely match VZW.
But rather than wait for another "double data" offer, I'd suggest you just determine your actual data needs, and look at the total cost compared to what you are paying now. I have noticed that as data prices have come down, those unlimited data plans are more expensive to hang on to.
And be aware that the new plans include unlimited minutes and unlimited texting. I'm convinced that as time goes on, data will become less and less expensive, but the cost of those old unlimited plans won't change.