Wow, that's a lot of activity here since yesterday! Let me try to address as many points as possible.
Some of you have been wondering about the country setting. Well, I initially got 2 MAC addresses to begin with, and the first one didn't work as expected, it beheaved like a "fresh" address - i.e. my first 3DS got nothing, and the second one got the first. Obviously the remote relay didn't quite work as expected. Instead of wasting the second MAC, I tried to figure out what other parameters Nintendo might be looking for. After some googling, I found that hostapd (the Linux SoftAP software) has a field called "country_code", so I thought it would be worth a try. Changed the country code and it worked. Maybe Nintendo does some pre-sorting according to this, since it slightly reduces the work required to browse through a server-side database. Maybe it's just a per-continent thing.
It seems like there is a MAC-based delay of 8 hours, similar to regular StreetPass tags. I would guess that this limit is implemented on the 3DS end of the mechanism; otherwise, a few thousand units sending several requests per minute could possibly bring down Nintendos servers in no time.
I am currently reworking my script used to emulate relay points so that it is more reusable; those of you who have a working Linux system should find some use for it. Since we now have a few additional MAC addresses, I have the opportunity to try a few more things before I post it.