SPI to USB and Terminal
spi isn't the best way to debug stuff,because you can't hook it to a pc,and you need to convert it to something else, and if you want to debug something you don't rreally want more layer of "possible problems".

IMHO you should use something more standard like jtag debug or a logic analyzer but if you really want to use the spi you can use a bus pirate or you can use an embedded system like the Raspberry of the beaglebone, in this way you can have access directly to the SPI via the GPIOs.