Xbox 360 controllers suddenly stopped working correctly on the new Pi3B+. Some quick Googling revealed this to be an on-going issue for the past few months that only just now filtered down to me. Performed a quick swap back to the Pi3B and everything is working fine. So, now the 3B+ is my “DEV box” for OpenCV. Because the GPU was not bumped up in this version, there was not really any major increase in N64 performance, so NBD.
Also, I bought a new case for the RetroPie:
The power and reset switches actually work! It goes through a graceful power-down, saving game states, etc, as it goes down. MUCH better than ripping the power cable out of the Pi, which is the standard way to reboot the box.
I paid an extra dollar for the Pi3B+ version and ended up having to use it with the Pi3B.