Thanks for your answers!
Some followup questions:
I checked out transmedia site (transmediacard.com) as well as dalc.com - can't find any info on actually getting miles with these programs, only cash back. (mileguy mentioned, "lets you apply your miles to CO, US or UA".) Either way, they're $49/yr, and I'll probably barely make that up by eating at the participating restaurants, while the airlines' mileage programs are free...
dgordon, you're right, I overlooked the fact that 500 miles bonus is only for elite members. (That info is under special offers in earning miles section of aa.com.)
I think the verdict is, register one card for one airline's program, and another card - for another.
If I register a mileage card (such as Compubank debit Visa) for an airline's dining program, I should get 11 miles per dollar, correct?
Thanks again.