While technically, 2 credits at a signature is less efficient than two 1-credit meals elsewhere, it's still pretty easy to get your DxDP credits value worth at signatures. In fact, many DxDP users recommend one signature and one single TS meal per day, rather than deal with the amount of food (and time!) three sit-down meals would entail.
As noted above, for 2017, the break-even price per credit on DxDP is around $32 or so, it goes up to $33-$34 in 2018. Given that appetizer and dessert are included (and even an alcoholic drink in lieu of a regular drink in 2018), you'd almost have to be trying to be unoptimal in order to not break even or better most of the time.