I'm a SEA GM, here are my upgrade stats so far this year:

FC: BOI (12/12), GEG (6/6), RDM (2/2), EUG (2/2), LAX (2/4), SLC (1/8), DEN (2/2), MSP (0/2) SAC (2/2), HNL (0/2). I haven't gotten FC upgrades onwards out of SLC or MSP.

C+: Everything else except HNL (middle seat for all the hub flights).

I think down the coast you should get some, certainly anything regional you'd have a great shot, I wouldn't expect any upgrades on anything longer than that, though.

If you want to get an upgrade to FC from SEA as a silver, just fly to Boise! But, then you have to go to Boise...