I have been playing Streetpass Quest and the Puzzle games for two years now. I've never gamed the system and I won't. But I wouldn't call it a 'slow burn', more an endlessly frustrating parade of misery. I really think that these are some of the worst ideas Nintendo has ever had.
I've taken my 3DS everywhere for two years. Commuting to work in a big city (by train, 30 minutes), every time I go to a game store, on my trip to the Nintendo Store in NYC, in airports etc. In all that time I've had 80 hits. I just about beat Streetpass Quest II using coins and the special Iwata Mii, and it was a soulless, joyless experience. You only get 10 coins a day, so it takes a few days to get enough to build a decent team. You enter the dungeon, and the enemy has only a slice of life left. You kill it. You enter a room, darkened, poisoned, iced, whatever. Each of your guys turns and leaves... days of totting the 3DS around wasted. You want to smash your DS into little pieces.
So fuck it, you think. I'll spend coins on the puzzles. But you get a piece you already had 90% of the time, even when you have entire panels lying almost entirely bare. On top of that, you'll never get enough pink pieces to enjoy the excellent dioramas you're trying to unlock. But what's this? You go on a flight and pick up three passes. But guess what? None of them have puzzle pieces for you.
It's masochistic, and it makes me feel bad every time I use it. And rather than making me feel like I'm part of a community using DS, it has reinforced that I am the ONLY one carrying one around. I worked next to GOOGLE for a year. GOOGLE. They had Mario Kart posters in the windows. Only got about 4 streetpasses from google employees in the year.
Fuck streetpass.