I think the idea of turning the Pierce Elevated into a High Line type of park is a good one, but I think tearing it down and re-stitching the street grid is an even better idea. Perhaps even incorporate a linear park like the Koreans did with Cheonggyecheon in Seoul: http://inhabitat.com/how-the-cheonggyecheon-river-urban-design-restored-the-green-heart-of-seoul/