Further on, it notes that big impeller drives wreck small ones without being harmed in turn. And that counter misses purposely use their wedge to blow up other missles.
Indeed. You'd need something fairly large to take out an SD by wedge interpenetration. Going off the official chart in
Ashes of Victory:
A counter missile needs to be about a tenth the size of what's being taken out, so about 150 meters long for an SD. Apparently counter missiles have large wedges relative to their size than normal missiles since that's their means of attack.
This wouldn't be as cheap and disposable as a missile for sure, though for taking out an SD it would be well worthwhile. Of note, however, rather than hit the enemy wedge if you hit their
sidewall with your wedge you do vastly more damage and there's no such size limitation, everything hit by the wedge in that situation is vaporized. Since all the other missiles have to hit the sidewall (or hit with beams they fire in the case of laserheads and graserpedoes) to do any damage anyway that would be the preferred way to use wedge missiles.
Oh, now I see. I imagine they weren't developed because they break the setting too hard.
They're too big to fire out a missile tube and nobody ever thought to build a bigger missile tube because... um... they'll get back to you on that.