The MiniX Plus has a slightly different board layout, with the PCB flipped and, on some models, 1GB DDR memory. If the DDR speed is the same is unknown. The other components, like the AV connector, voltage controller, CPU and Wifi stayed the same it seems.
The date on the MiniX was 2012.05.14 (all versions, Miniand/Pandawill/Dealextreme) and the MiniX Plus is dated 2012.06.19.
Thanks to Yangxi for uploading this, the image is clickable.