Be very careful with Crazy/Super Glue! Off the top of my head, I can see three serious dangers in attempting to repair it yourself:
1.) Speaker damage! The same capillary action that draws the glue into cracks on contact could easily draw any excess into the speaker (either the coil or the paper cone -- if it is paper). Think of how nasty the speakers sounded when we had the common occurrence of garbled sound in webOS 3.0.4, and expect to hear that for the rest of the TouchPad's life, if even a small drop finds its way to the speaker.
2.) The glue could make future repairs (like battery replacement) much more difficult, if the glue creates a bond between the back and a component that shouldn't be bonded.
3.) Any cyanoacrylate glue flows more easily than water. Injecting what may appear to be a drop could be enough of a stream to drip into the electronics of the TouchPad, which would make for a very bad day.
I agree with the premise that those of us with cracked TouchPads (myself included) should take some action to prevent further damage. I just believe that the safer way to go might be an outer case.