There is already a destination in the area you're talking about, just one that gets very, very little attention, due to its location in a nondescript warehouse--the California Auto Museum:
http://www.toweautomuseum.org/
Unfortunately they aren't really a part of the current Docks plan, but they certainly should be. It would be a shame to lose a well-established transportation meeting, especially because the CAM has really stepped out in recent years to hold more public events (like the CAM auto show in Midtown, its series of concerts and drive-in movies, etcetera.) One semi-dream idea of mine is for the CAM to have a big, highly visible space in the new Docks, like the Petersen Auto Museum in Los Angeles. It would neatly bookend the area, with the Powerhouse Science Center just north of the I Street bridge, the Railroad Museum and Sacramento History Museum in Old Sacramento, the Sacrament Southern Railroad south into the Docks, and the newly expanded Crocker just across the pedestrian bridge over I-5...not to mention the planned Indian Museum that will go into the northern end of West Sacramento, to reel things back towards the thread topic.
I can see Old Sacramento taking issue with a modern bridge plopping people in the middle of the existing Old Sacramento waterfront and wharf. Improving the I Street bridge, making it more useful to pedestrians and bicyclists, would help move folks from the existing (and increasingly dense) neighborhood around old Washington.