Rio Washingtonian Center has announced plans for a $30 million upgrade over the next two years, including improvements to the boardwalk and pedestrian bridge, a new performance stage and a redesigned lakefront seating area. An indoor/outdoor Silver Diner will open along the water next summer, joining a list of upcoming tenants that now includes Yard House, Dave & Buster’s, Lanzhou Hand Pulled Noodles, Kung Fu Tea and The Baked Bear. And the AMC movie theater is almost done with a renovation of its own: Snazzy new reclining seats, an expanded menu and a bar are all set to debut next month.