The only downside is the connection type for the switches that I've chosen, a simple 'plug & play' solution would be nice but the current version has screws that hold each cable. Not the biggest concern, since I can easily put better connectors onto the cables themselves.
I've also put little rubber feet on all boards so that they are elevated a bit from the surface and also get a little more protected from vibrations and shocks. The ribbon/flat cable design I've chosen showed to be extremely nice when debugging, as the board constantly moves from the cabinet to the workbench! I'll probably do this on the solenoid board as well in the future.