As for fpgaarcade, Im not nearly as informed as some, but I was under the impression it's somewhat more "ambitious" (for lack of a better word) than minimig.
Could be; there doesn't seem to be much at all on the site about it, so maybe it's one of those projects (like Natami) where most of the information is on forum or blog posts and I just haven't encountered it.
In any case, there might be more overlap than I thought, but I still think both projects have clearly distinct appeal and target markets (such as those would be, with no actual marketing.) FPGA Arcade is obviously aimed towards retro gamers, seeing as the Amiga functionality is only one of a variety of platforms supported, while Natami is aimed squarely at Amiga fans and aims to support one system
extremely well. Not saying that there's no overlap, but I'm thinking there's certainly room for both in the world.