I think Alaska should make PDX into a real hub, with operations approaching that of SEA.
There are a lot of midwestern and eastern cities which do not receive non-stop service from PDX and many others to which there is no competition. I feel Alaska would have no problem filling one 737-700 daily (120 seats) on many of these routes.
Why should Alaska risk entering new markets?? Well, simply put, Alaska has no room to expand within most of their existing markets. Alaska is seriously short on gates at all of its hubs EXCEPT for PDX, and they already have considerable marketshare on almost every route they serve.
Why expand out of PDX?? Portland is a well-designed, modern, uncongested airport and it's not a hub for any major airlines. Not surprisingly, Alaska's on-time performance out of PDX is consistantly the best out of their hub airports. IMHO, PDX is by far the most desirable airport on the West Coast for a carrier looking to expand.
Alaska and Horizon already have the most flights out of PDX, but they only serve a limited route system. I really see no reason why some carefully-planned entries into new markets won't be a tremendous boon for the company.