Thanks for the followup, Guy. It will probably be very helpful for most users working on this. In my case, the power button code is apparently listed and possibly deactivated somewhere else. As I mentioned above, cat /proc/acpi/wakeup | sort shows everything disabled. So I guess that's also why your suggestion of grep enabled /proc/acpi/wakeup silently returns no output. Wish I could recall where in my system there was an entirely different listing of device codes, and whether one of those gave some indication of relating to the power button. Anyway, the bottom line for me is that with everything disabled in /proc/acpi/wakeup the keyboard and mouse no longer wake from Suspend but happily the power button does. 
Thanks again for your code clarification, and especially for offering an improved version for others seeking a solution.