there is always a tradeoff. I too live in Seattle but fly other places from the west coast. Just for simplicity I like putting Delta, Co, NW, and AA on AS as when I want to use the miles AS is so much easier to book reward seats. The 50% mileage benefit doesnt hurt, nor does the fast lane into security. Now with AS flying to Hawaii it makes it pretty easy, but yes you lose some benefits when flying other carriers.