Complex sentence: In 2000 to 2003 the Lighter Basin was redeveloped as the Viaduct Basin, which served as a headquarters for the various yachting syndicates involved in the America's Cup campaigns of 2000 and 2003, and is now an upper-class (multi-story) residential area.
Split into simpler sentences: In 2000 to 2003 the Lighter Basin was redeveloped as the Viaduct Basin, which served as a headquarters for the various yachting syndicates involved in the America's Cup campaigns of 2000 and 2003. The area is now an upper-class (multi-story) residential area.