My old control panel had no admin panel, everything was done with shift type functions. (1P + 2P + UP = exit, 1P = load, etc). This method works fine and keeps your panel feeling 'authentic'. Except you will need some visible instructions on how to operate the functions. If your like me, you will have lots of friends using your machine and it gets kind of annoying explaining 10000000 times what the different functions are.
My new panel im making has 4 admin buttons, these are my decided functions:
1 = open game
2 = vol down
3 = vol up
2 + 3 = exit game
4 = pause
As for the pause button, i never had one previously so whenever i got a phone call etc i'd end up opening the drawer and hitting P on the keyboard to pause. Now I want to keep my keyboard locked and only opened when necessary, so i copped out and put the pause button on the panel.
As for save buttons, i say no, never. Not for MAME. Arcade games are meant to be played in one hard session from start to finish until your wrists hurt, eyes are straining and your mouth is soo dry that you can taste cheese in the back of your throat. Pause button is as far as i will go, save/load is ghey