As far as the credit cards, I just switch between the WorldPerks and the AA credit cards on an annual basis. Once the annual fee nears for one card, I switch to the other and receive the 5000 bonus that comes with it. I've been doing it for about ten years now and have never had a problem.
As far as Dining for Miles, I register two different credit cards (in addition to my NW or AA credit card, I have a Hilton no annual fee card). One credit card accrues WorldPerks and the other AA Dining for Miles. I receive AA miles for one meal each month and NW miles for a second meal each month at each of my favorite restaurants. Sorry for the confusion.