Something odd happened today: after having 1 play coin left over last night, I just noticed that my 3DS said 280 coins this afternoon.
After getting my 3DS repaired (well, replaced technically) it arrived back in my hands yesterday. While checking to ensure all system settings were carried over correctly, I noticed that I had a few play coins left over and spent 10 of my 11 coins trying to get a bit further in Find Mii. Today I didn't do anything meaningful - played with Rytmik Rock Edition for 30 minutes at lunch, checked out the newest games and videos in Nintendo eShop, and carried my system around for a bit. So it was a surprise to see my play coin account with a huge boost!
Has anyone else noticed odd things with play coins? And now that I've got 'em, what should I use them on? [Edit: 280 coins spent, and now I'm halfway through the final ghost in Find Mii.]