Are there risks in connecting the power pins of separate development boards?
If you are connecting two boards (powered from two different wall adapter), make sure you have made ground common. Short the Ground Pins of two boards together. This way, both boards will have common reference.  

Unless you are using the 3.3 V from first board to power the second board, you don't have to connect the power lines. Once, common ground is established, the voltage levels definition remain same for both boards. 3.3 V for one board now means 3.3 V for the other board too.