Thanks for the comment, Rina!
Slight update (same test leg, different angles):
Considering that I went to the trouble of getting those armored-looking lower legs -- and that there's not much I can foresee doing with the dinky left forearm armor pieces from Super Shredder -- I'm thinking maybe I'll just cut those spikes off and glue them to the legs. (Right now they're being held in place by poster tack.) It'd be more along the lines of Cyber Shredder's leg armor, and it would let me keep more awesome Super Shredder leg armor pieces for future customs.
My only concern is that the lower spike could limit the forward ankle articulation.