Actually, Martha gets quite a bit of play in some other stories - specifically, the ones by Jeff Loeb and Tim Sale. In a Halloween story with the Mad Hatter, it is revealed that Bruce is particularly disturbed by the Hatter because he perverts one of his final memories of his mother - that of her reading 'Alice in Wonderland' to him just before they started out for the movie theatre. He gets knocked out and dreams about this, and wakes up sobbing "MOTHER! Mother..." Then, during 'Long Halloween', he gets a jet of the Scarecrow's fear gas right in the face, and gets a delayed reaction from it - he starts hallucinating that his parents are still alive, and that everyone is Joe Chill in the alley, seeking to kill them. When the cops come up to Bruce Wayne's doorstep to arrest him on suspicion of murder (long story), he panics, and runs - but not with his 'parents', with his MOTHER. He keeps repeating 'he wanted the pearls', and 'they'll never find us, Mother'. When the cops finally track him down, he's sprawled across his parents' graves, hugging Martha's tombstone and weeping like a little boy. The last words of the issue are 'We made it, Mother... we made it.' It's pretty emotional stuff. I don't know about the rest of the DCU, but in Loeb-canon, Martha Wayne is VERY important to Batman.