If anyone else was getting frustrated getting MAME running on OS X, the folks at OpenEmu apparently have it figured out. You have to download the “experimental” version to get the MAME integration.
Having so much fun with this. Bought a clearance PS3 joystick for five bucks to play these things without the keyboard… and perhaps most importantly, I figured out the issue I’d been having with ROMs sometimes working and sometimes not, and successfully downloaded a complete set of the correct version ROMs. OpenEmu is chewing on 15,000+ ROMs for our playing pleasure…