I can never understand why anybody would use anything other than a PC for a MAME cabinet.  
-   Best platform for general MAME development support
-   Absolutely unrivaled in power, dollar for dollar 
-   Great selection of front ends
-   Enormous community of other folks using PC’s who can help you get up and running because they’re using the same platform
-   Easy plug-and-play for peripherals like iPac, speakers, etc.  
-   Easy to connect to any type of display
-   Highly customizable (hiding splash screens, etc.)
All of these benefits, and a totally capable machine (for the purpose at hand) can usually be had from your local classifieds for $20-$40 or so… heck, you may even have a friend or relative willing to give you an old PC for free.  
I can see how really small projects may require a physically compact hardware platform such as a Raspberry Pi or Ouya, but even there I’m guessing a bit of up front planning and cost/benefit analysis would go a long way.  
I can also understand the temptation to re-purpose some type of hardware for other nerdy uses, but ultimately you need to ask yourself what you’d rather have: a neat DIY science project (“hey, look what I made out of my old crappy Mac laptop!”) or a versatile, kick---I'm attempting to get by the auto-censor and should be beaten after I re-read the rules-- MAME cabinet?