kg4wsv I2C would be a better candidate.
Up to 128 sensors with only two wires.
SPI has two distinct advantages: SPI is much much faster that I2C (25MHz vs 400kHz, IIRC), and, in this case, the thermocouple interface ICs are only available in SPI. 
On the number of nodes on the bus issue, I have noticed many ICs that have fixed addresses, or allow only a few bits of the address to be set by the designer, so practically this limit is usually much lower than 127. For example, the DS1631 that was discussed on the forum recently has 3 pins (3 bits = 8 possible addresses) available.
-j