--Ordered Teensy 3.1 microcontroller board (72 MHz ARM Cortex-M4, 256k flash, 64k RAM, 34 digital IO pins--all interruptable, USB interface to PC).  Not sure if it will be capable of running both encoders from one Teensy, so I ordered enough to put two Teensys on the rover, with spares.  There seems to be a fairly active dev community for the Teensy, with an already-existing Encoder library built for quadrature encoders (code appears to be all in C).  These boards were surprisingly cheap, <0/board.
--Installed longer whiskers on bump switches.  Rear switches seem to be working fine.  Front switch whiskers sag down in front of the ultrasonic sensor, which will render that sensor useless.  I need to figure out a way to keep the whiskers clear of the sensor.  The first thing I tried was to mount an old whisker sticking out the front of the rover for the new whiskers to rest on (above the sensor's path), but that doesn't seem to work to well--the new whiskers don't move as freely as they need to.  One thought is to use a smoother material (metal?) for the whisker rest to reduce friction.  Another thought is to move the ultrasonic sensor to another location--possibly mounted on top of the pan/tilt camera.  That might prove more useful, giving a distance to whatever the camera is looking at rather than a distance from the front of the rover.