Just wanted to bump this, see if anyone has had any success. I can get the nag screens and background via scripts, but no luck enabling wifi yet.
I've enabled Wifi with the USB scripts, as have may others. Your post doesn't provide enough information to formulate any specific troubleshooting advice, but it most certainly works.
Indeed, the "common tweaks" USB script was just updated a few days ago by the author over on the Mazda3 forum. You might try the newest version.
Personally, I don't see the benefit of enabling Wifi, other than as a failsafe for SSH in case I was doing extensive editing of the system beyond the common hacks (which I'm not). There are currently no applications in the U.S. system that use internet data.