Thanks very much for everyone's input and advice, and to onebuck for moderating. So far, the best I've been able to do has been to mount the original ddrsecue image as a "loop" and grab files from there. Meanwhile, since I have that image to work with at the very worst, and I'd better add a disclaimer before saying this ...
*** DISCLAIMER: DON'T DO THIS! DON'T DO THIS! DON'T DO THIS! ***
... since the drive appeared to be pretty much dead anyway, I gently smacked it on a desk a few times, put it in a sealed bag and in a freezer for a few hours, put it back into my external drive dock, and tried another ddrescue on it. It got up to about 33 GB over the course of a day or so before it slowed down to about zero I/O again. I'm going to try this process a few more times (interrupt ddrescue, gently beat up the drive a bit, resume using the ddrescue log) until it stops responding completely.