Some of its feet get temporarily stuck between keys, springing loose again as others push down. It has no trouble whatsoever with this obstacle, nor with any of the others on my cluttered desk - even though it is still utterly brainless. As the feet rise to a maximum of 2 cm off the floor, a cassette box is about the tallest vertical obstacle that the Spider is able to step onto. Another limitation is slope. When asked to sustain a climb angle of more than about 20 degrees, the Spider rolls over backwards.
Improvements are certainly possible.
A better choice might be more legs, like 10 or 12 on a longer body, but with the same size gear wheels. That would give better traction and climbing ability. Make a gear shaft the center of a nice, tight hinge joint. Then the drive train will function as before. Using the third motor and a suitable mechanism, the robot could raise its front part to step onto a tall obstacle, somewhat like a caterpillar.