An idea I'd cooked up for something like this had four springs mounted on the bottom of each panel, recessed into 7/8 holes so that if the panel lay flat on the floor or something, they wouldnt get bent or crushed.
The cab would have four copper pipe caps (3/4 inch caps from the plumbing section at home depot), attached to wires leading directly to a USB port on the PC.
The springs would make a good contact with the caps, and the caps themselves would act as a guide with the recessed holes in the panel. The panels could then all have a cheap USB hub.
Only having four points of contact (actually, I'd thought of 5, one just being a large field ground) would make it much more robust, since the more contact points, the greater chance of failure.
Electrically I think it would work fine, since none of the stuff I would hook up are "high bandwidth" devices. An external HDD on a USB2.0 port might behave a little wonky, but a joystick should be cool.
The downside, of course, would be that each panel would have to have its own USB encoder.
But, the way I figured it, each panel would be completely different, and it's very hacker friendly - ie; get a cheap USB steering wheel, hack to make a driving panel. Hack a cheap USB mouse to a trackball, etc.. Hack a cheap USB gamepad or stick to make a more standard arcade panel. My plans also called for cheap usb headphone ports, for silent playing. Easy to add a usb socket to plug in a keyboard/mouse for testing and setup, or a usb pendrive to upgrade the software (or network card, etc - you see where I'm going with this).
Dont forget, XBox accessories are all just USB, with very good homebrew drivers about (btw, my XBox S-type controller with hacked cable is *the best* gamepad I've ever used on the PC), so there's plenty of gaming junk in the bargain bin at EB. I also considered using an XBox as the brains of the cab.
It seemed cheap, easy to source (parts all at home depot, a dime a cap and pennies a spring), very rugged, and very doable.
I've since backed off on making a mame machine, deciding I prefer rebuilding dedicated uprights, but if I do eventually build one, some sort of removable panel is necessary.
I find nothing really "authentic" about some cluttered panel with 90000 buttons and 4 kinds of sticks and spinners and trackballs and guns and steering wheels and waffle irons. The whole point of an arcade cab is simplicity - it should be obvious how it works and what you're supposed to do the first time you drop a quarter in.
Hell, I even find neo-geo games that dont use all 4 buttons a little hokey. That's just one guys opinion, though.