Any other options for getting 50+ digital inputs?
When my only tool is a hammer everything looks like a nail, but... 
You might want to consider using something like the SPI 8-bit I/O expander MCP23S08 (sample-able) from Microchip, I've written about my experiences here:
http://code.rancidbacon.com/LearningAboutArduinoMCP23S08
(I have intentions to turn my rough code into a library, but...)
More likely you'll want to use the 16-bit MCP23x17 variation which I have on hand but not yet tried.
With the 16-bit version presumably you could get 48 (or 64) inputs with 3 (or 4) chips and only need one SPI chip-select line as you can address up to 8 devices using the one chip select line. If you're more into I2C you could also use that although I haven't tried it.
The bi-directional nature of these devices might be overkill for your situation--I have no idea of the price difference between these chips and what you were already considering.
Other potential solutions might be to lay your switches out in a matrix to reduce the number of inputs needed or use a resistor-ladder type arrangement with an analog input. I guess it depends a little on the switches you're using.
Hope this information might be helpful.
--Phil.