I don't believe in loyalty to a business entity. DL's only loyalty is to increase revenues and profits. The only reason they have elite benefits is because it's a marketing and customer retention tool. Those who believe in loyalty to a business deserve to be fleeced.
Even if you're happy with DL, you should still run the numbers now and then to make sure you're getting a good value compared to the market.
To the OP, you may be better off looking at VS or AS for a FFP program and SPG for affinity card use.