I should have caught the current requirements. I guess I assumed that since other effects were working fine across all 64 LEDs that must mean it's a software problem. But those effects didn't have all 64 LEDs constantly lit either, and they did exhibit some strange behavior when I switched from USB power to a separate (9V, 3A) power supply. So that's probably it.
My power supply can be switched to 5V, 4A, but the Arduino won't run on that will it? If I run the Arduino off a USB or 9V supply, then run the SPI pins through an optoisolator and power the LEDs with the 5V supply, that should work, right?
Re: the infinite loops, hey, I've just been trying to get the damn thing to work. 