I got my 3DS for Christmas and stumbled on this thread while, out of frustration for the very slim pickins for StreetPass in my area, researching ways to get more tags.
I had an old DD-WRT router that I had converted to a switch after running out of ports coming out of my AT&T router upstairs and my downstairs WiFi access point, so I turned the WiFi back on, set up the "attwifi" with the MAC Clone settings, restricted access to only my 3DS' MAC address (since it is unsecured and public), and boom, it has worked perfectly as far as getting guests at the Mii Plaza. Awesome info provided in the OP.
The only thing I've noticed is that I'm not getting any Shadow Link alerts for ALBW. I don't want to burn myself out by "cheating" too much and killing the fun of getting Streetpasses out in the wild, so I've just cycled between the main MAC (ending in .46) and the ALBW MAC (ending in .43) once or twice a day. Both are getting me Mii Plaza guests, but neither are getting me LBTW fights. I have gotten 2 or 3 from around my city, so I know I have it set up correctly. Is there something else going on, or am I just having exceptionally bad luck with the two HomePass addresses I'm using?
Come to think of it... I have it turned on for Fire Emblem as well, and I haven't gotten anything there either. I'm only a couple of fights into the game, but I do remember getting a couple of StreetPass alerts on its icon before as well.