I setup streetpass router mainly as a curiousity after reading how it worked. I grabbed about 9 or so 'legit' with 5 of those coming from the local booze store when I went to get my wife a bottle of wine on the way home one night.
If you have a second hand router or buy one for ~$5 at a Goodwill or salvage PC shop, it's trivial to setup the streetpass router. I had Cisco 160 that locks up intermittently that I took off a client when I replaced it with a new 320. It took me a few minutes to flash it, setup a MAC filter to only allow my 3DS XL to connect. Since then I've seen a few hundred streetpass miis land on my handheld. For the most part, I don't care but I did fire up Zelda after taking a month off and the little yard where signs from visitors appear was full. I haven't seen a single person come through for the Bravely Default demo though, but I heard there's a trick to getting your 20 in the game itself. The amusing thing is that after I setup the 160 with the new dd-wrt firmware, it hasn't really locked up since, apparently Cisco overclocked the thing for whatever reason and flashing it with dd-wrt 'fixes' that.
For the most part it seems useless, you can collect the little picture panels and unlock 3d images you'll look at once and never look at again, and the find mii game is pretty dopey if you're over 12 but at least my mii has a Samus helmet now. Lots of time I click through my 9 or 10 little visitors and think to myself, "Wasting your time" but I guess I may as well keep at it - it's easy rupees in Zelda when you murder someone's shadow Link for a bounty.