Yeah, one of my third gate ideas has always been Yesterland. But I think Yesterland attractions are only part of it. Rather than recreating the park on the exact same layout and whatnot, break it down into other themes. One area would be extinct attractions. Of course, with today's engineering capabilities, you could build Nature's Wonderland on top of the Submarine show building and take back some creative license in how you present the Yeaterland rides for a new generation. Then you create a land devoted to Yesterland Disney television. Use the Indy ride concept to create a Davy Crocket ride. Put on a Mickey Mouse Club stage show, and have a second little theater, sort of like the Main St. Cinema, where you can go and see actual episodes. Then, no Yesterland is complete without the Imagineer's Drawing Board. Create the Museum of the Weird, the Chinese restaurant from Residential Street, and all sorts of attractions that never made it off the paper.
As for Main St., I think you almost have to go for the Anaheim '55 look. Start evoking the era before guests get to the hub. And then have them pass under a sign much like this: