Lounge memberships are 100% worth it. With an Alaska board room membership you can access the Cathay Pacific lounge at SFO as well as any American Admirals Club (which aren't generally anything special).
Unlike the Cathay lounge at SFO (T-I A-gates) the Centurion is at T-3 so not only can you get in from T-3 but from T-I G-gates via the airside bridge (no need to re-clear security).
The Platinum also gets you into Delta lounges, and you can request a Priority Pass Select (included) which gives you access to the Alaska lounges, the Air France lounge at SFO T-I A-gates and a lot of others, especially international ones.
I've started flying from SFO to most places via DFW just so I can hang out at the DFW centurion ;)
The lady at the desk said if we applied right there she would have let us in. I'm more of a cash back person though. Can't be bothered with points or fees.