"Just to be clear, have you removed all external connections to the reset pin now? To program the device properly, the programmer needs to be able to toggle the reset pin, at least according to the AVR specs " :
As of now, there is nothing attached to the nano but power and programmer.
"Did you connect anything to board's SPI pins between the time when you successfully programmed it and the time when programming failed?" :
I did have a separate nano(which I can still program) hooked up as slave after loading the Master SPI code. The connection between the two chips was via standard SCK, MOSI, MISO, SS pins. They did appear to be sharing data, but I was not getting the numbers I was expecting. I was trouble-shooting this when I ran into the programming problem.
"When you say you programmed the board to be an SPI master, you mean in software, right?" : yes
"Did you change any of the fuse settings?" : If I did, I don't know how. However, as mentioned to David the SPIEN fuse is not checked on the AVR Studio Fuses page as it is on my other chips, so perhaps I did, but not because I did anything intentionally to make this change.