DL probably isn't making a big deal about it because it really isn't the last DC9 flight. It's the last DC9-30, the end of flying for a sub-fleet. I understand the significance, but I think it's more of a milestone when the last DC9 stops flying for DL for good. THe DC9-40 will fly for a few more months and then the DC9-50 will fly for a few more years.
Do you have info on routes the 9-40 tends to frequent? Would like to get a trip in before those go as well.