Mefustae, all good points, but you missed a critical part of what I said--'terminal engagement.' That means the final portion of the missile's attack, when jamming and evasive maneuvering have failed and the last line of defense is shields. It assumes the missile has already successfully tracked to target and has a collision vector. The missile travels at sub-light speeds so it can maneuver. Once a hit is certain it accelerates to C and pretty much becomes a MAC projectile, smashing into it's target for massive damage.
Headdie brings up another good point. At long ranges an attacking fleet could just jump out of the way, but at normal SW combat ranges, these would be inescapable. I guess that means these wouldn't really work as a stationary defense, but a ship armed with such a missile would scare the piss out of any sane captain.
And good point--how the f*** do hyperdrives work?