As it has been said on this board before, by people who know about what matters when it comes to ratings, the true test of any new station or format will be how a station performs over a four book average.
Another thing to consider is whereas the Latino listener is typically VERY loyal to their favorite station(s), from a business standpoint, selling spots to advertisers in markets like a Seattle or Portland, is more difficult in spite of the growing ratings and loyalty of the Spanish-speaking listeners. Many advertisers just don't get it yet. I'm sure that will change over time, but flipping a full-market FM station to Spanish right now means there will be several months, if not years of slow advertising ramp-up. Most radio companies are hanging on by the skin of their teeth right now with the economic softening of traditional media, and I doubt any will be ready to jump into Spanish programming in the PNW in the near future.