What are my options for interfacing **30** incremental encoders to an MCU?
A small FPGA is the way to go here.  You would need a very large CPLD to manage this many encoders - they are not useful for much more than glue logic.  Generally a CPLD gives you one flip-flop per pin.  An FPGA has logic resources that are specifically designed for building things like accumulators and shift registers, and far more of them than a CPLD with the same number of pins.  For 30 encoders with 16 bit counters on each, that's a minimum of 480 flip flops just for the counters, not counting the encoder processing and SPI interface.  I would suggest a small Spartan 3 or Spartan 6 - they are available in TQFP and should be easy to interface with.