Given what I know about the Digital Sidecar, I don't think you'd be gaining anything unless you installed a cRIO on the robot as well. From what I remember, all the IO pins basically wend directly to the module on the cRIO.
If you need more than the 10 IO and can't get an expansion board, I'd recommend using a multiplexer .
Example:
https://www.sparkfun.com/products/9056
Alternatively you can use an A2D as below for inputs over I2C. That might be the easier method.
http://www.adafruit.com/products/1083