This is only one instance so not sure if this really means anything but.................
I have one site that somehow has over 1800 google plus's. That particluar site has the same DA as another site that only has about 50 g+'s but has about 10x's the amount of incoming links. The high g+ site has the same DA as a lot of my sites actually that have many more incoming links by quite a high margin. So if DA and incoming links have a corelation, and DA and g+ have a correlation, I would derive that g+ really does help.
If that makes any kind of sense, what I am saying is many say google plus means nothing and I have always held the posistion that it does help, afterall it is a google product. So the only explanation I can come up with for the higher DA is the g+'s.
Just thought I would share. Not sure it really means much but it is the only explanation I can come up with for the higher DA.