Not sure about hyperspin, but right mouse click can open settings in some front-ends and emulators.
If you give guests or children any way to screw up your cab, they will find it.
It doesn't matter if it requires a combination of simultaneously pressed buttons or using a hidden shift button,
someone will accidentally do it and proceed to screw up your settings.
Your goal should be to make it impossible to make any changes to the setup without using a wireless keyboard and/or mouse.
Also make sure the power button is hidden.
I like only having Exit and maybe Pause. That's usually it.
I have two extra arrows on mine that switch between genre based gamelists because all the arcade games on my setup are divided up by genre (using Mala as a front-end)
Since you've got the extra spaces, you could do volume up/down, maybe even mute. Sorry if I missed what interface you are using, but I think the Ipac can be mapped for this just like the volume buttons on a media keyboard.
You could do save and load, but then MAME will ask you to press another key to choose the save slot. Also not all emulators support save states. (experiment with it first to see how it works)
You could do dedicated navigation buttons like Prev/Next Emulator
That's all I can think of at the moment.