Interesting. Is barbed wire overkill since the bag will rip before the barbed wire will snap? I wonder if a simple layer of sharp rocks inbetween layers would work ? (Pound the layer, then add the rocks. Just don't pound them in. Let them stick up into the next layer. Then when you pound the next layer those rocks, in the layer below, will tie the two layers together).
Several years ago I helped build a small earthbag dome using feed bags and barbed wire. Not too long ago, I heard about Hyperadobe which uses mesh bags and eliminates the barbed wire (which I found was a bit of a pain to work with). Wish I had know about it before but still am satisfied with our project.
Here is a link to Eathbag building.com that talks about it more: Hyperadobe
Something to consider anyways.
Chris, from my understanding, the bag is (mostly) there as a temporary form until the soil hardens up. The barbed wire acts a bit like rebar to help hold it altogether. Not really even needed unless your in an earthquake prone area. We are not in such an area but used it anyways on our first build just to be on the safe side.
The rocks you suggest would do something similar to help prevent lateral movement but don't know in comparison to barbed wire which is connected all the way around the row.