I've built my own cabinet (using 3/4" plywood, not cardboard :) initially powered by a RPi2B+, and later upgraded to a used PC but still RetroPie. I don't thin

I've built my own cabinet (using 3/4" plywood, not cardboard :) initially powered by a RPi2B+, and later upgraded to a used PC but still RetroPie. I don't think the power of MAME is much of a concern here. RetroPie doesn't just have a single version of MAME, it support several of them, including some relatively newer ones. And while it is true that I've found a few games (Star Wars comes to mind) that wouldn't run on the default MAME, they do work on one of the alternates. For the games MAME is trying to address, I haven't found anything for which the computational power of my RPi 2B+ was insufficient. I wound up replacing the RPi with a PC not because of MAME, but because I wanted better emulation of other systems like Dreamcast. And even there, with the used PC off ebay, it's running well.