first of all remember you should have 3 connections first is your Ethernet which has internet. second it your wifi device which you have to rename to "Wi-Fi" and the third one is attwifi. attwifi shares the Ethernet's internet connection. when changing the mac address your changing the address of the Wi-Fi one not the attwifi one. when you change the mac of your Wi-Fi connection it changes the address of the attwifi automatically because attwifi is just a virtual network that was made using the real Wi-Fi network.
Thanks for the clarification! I've had the connections set up as such, and am currently cycling through the Prime MACs, but have yet to get a single streetpass..