My version of an improved Lower Manhattan would include the Twin Towers rebuilt in their old locations, with the same general architectural style of modernist buildings with the same slightly gothic spin to them. They would just be taller, more modern and inclusive of all the required building code upgrades one could think of being applied over the span of time since the old complex was completed.
Buildings 3 and 4 of the current center would be preserved, but integrated into the larger complex. Austin J. Tobin plaza would be rebuilt for the modern era, that meaning top artists would have this as an option for an outdoor venue. Also, the hotel and residential aspect will be spoken for by a number of buildings throughout the site, expanding the number of uses that this complex has on a daily basis, without being an afterthought.
Brookfield Place would be substantially expanded and heightened, matching better floor-to-floor against other buildings and featuring a greatly emboldened design. No longer stumpy looking 1980s buildings, now Brookfield Place can also compete with the likes of buildings in Dubai, Hong Kong or Mumbai.
Essentially it's a retread of the eras that made New York City great in the first place, juat a good amount bolder and more brash. These are also my original images that I made.