IF YOU LOOK at projections for the Pacific Northwest, through the 21st century, a population equivalent to 15 Seattles will move into this "livable" corner of the planet. "We have one last chance to get this right," says Gene Duvernoy, president of the Cascade Land Conservancy. What is "right?" The answer -- strike a balance that preserves what makes us "livable." According to a recent Pew Research poll, spaces and cities of the West exert a powerful draw on Americans. Denver, Seattle and San Diego topped the list of where folks would like to move. So as not to wreck...