Dave -- just tried your frontend for the first time. It is EXACTLY what I've been looking for! Too many I've tried are not only overly complicated, but simply not attractive as a frontend for a cab. Thanks for the vertical support as well.
If you are open to feedback, I've read your notes and I don't feel that you should knock yourself out adding a setup/config interface. The files are very well documented and easy to use. My only suggestion would be somehow capturing and reporting any output from MAME/emu itself. Some of my games were reporting errors, and the only way to figure out why they weren't running was to run them by hand on the command line to get the output. If there is any way you can redirect and capture output from a sublaunch, that would be nice (maybe just add a key to show the last command line output).
Rich