I agree that Notre Dame was by no means great. Still, I think any win in South Bend is significant.
It hasn't been hard for USC to do of late I guess, but I sat through 4 or 5 horrid losses back there before seeing USC win in 1997 -- I think USC had lost 8 or 9 in a row back there. So maybe my view is skewed by when I went to school, but for me any win at ND is a big win.