Also, expect to only get like 1 - 5 streetpass hits a month, even if you take it out regularly. Move to japan and you can expect to multiply those numbers by about 100.
When I took mine with me to college (high school) to gather streetpass hits and earn coins for walking, I'd usually get 3-4 people a day, depending on how long I was at college for on the day.
But, I mostly got the same people again and again and again.
If you take it out with you when you visit places, like day trips to the zoo or other similar tourist destinations, you can usually grab quite a few people. Particularly foreigners, which is nice because they register as being from a different part of the world on your globe, and might be from multiple regions.
(I have more streetpass regions collected for Japan than the UK as the UK is split into 4 regions (I've only met people from England, not Scotland, N. Ireland or Wales) whereas Japan is split into like 50 regions. So having met 100 Brits I've gotten 1 region, but meeting 4 japanese people I've got 3-4 regions).
There are also Streetpass groups you can find and join on Facebook/Twitter for your region, and provided its got enough members and activity they can do semi-regular meet ups, so groups of 3DS owners can all streetpass each other, play games, chat and socialise.
So if you do have a few Mii Plaza games but your town is a 3DS deadzone, you can still build up your Plaza population if you travel a bit.
