Paine Field is awesome, partly because I can drive to it in less than 15 minutes, but also because it has that regional airport feel, is brand new and is just overall very nice. I have moved all my flights there (I mostly fly to CA), and would even consider starting an international flight there and doing a layover in SFO than flying out of SEATAC. In fact, I am flying to Hong King next month using that strategy.
As far as expansion, I think it will come but will be a while. I've heard rumors from multiple sources that Alaska plans to expand, but I'm sure that will be based on demand and the willingness of the local community.