Just my opinion, but streetpass is sometime buggy. I have a friend who sometime comes to my home and we watch movies and play video games. He brings his 3ds along everytime. We always do firmware update. In firmware 2.0 I could get a SP from this friend an hour after he quit, even if we already had one when he entered the door 5 hours before. He never got that. It happened atleast 5 times within 2011. We also change mii color to adapt to Find Mii Quest RPG (or something lol) but it would sometime take 2 SP to update even tho the personal message was update. It was possible to get 3 SP a day, 1 every 8 hours. In fw 2.x, my 3ds would light green from a SP but no blinking icon in the system menu bottom screen,
Now since firmware 3.x, we seem not to be able to get that many SP a day. I always wonder what would happened if 2 people in the same house have a 3DS ?? SP slot would fill up quickly. This should solve the problem I think or atleast temper it. Also, me and my friend done 130 SP togheter since launch day, but mii character in the mii plaza now always say "It's the 99 times we meet!" (my 3ds is set to french). Oh weird stuff again. My friend arrive to my house and I am playing MK7 so to greet him I put my 3ds to sleep not closing MK7.. no streetpass for atleast 1 to 4 hours. We tested that a few time within the last 3 weeks and we got the SP within 1 to 4 hours after he arrives.
Sorry for my bad english, I am weed stone.
Pip'