For more than a decade, civic leaders and developers here have envisioned a large-scale redevelopment of downtown Los Angeles’s main civic and cultural thoroughfare, Grand Avenue. This past summer, the first — and smallest — component of this vision finally opened to the public. But instead of a massive mixed-use edifice that would completely change the streetscape, it was a modest 12-acre space named Grand Park, which replaced an existing but unwelcoming civic center plaza. The park was paid for by $50 million from Related Companies. Community leaders, real estate magnates and urban planners hope the Grand Avenue Development Project, which would add several million square feet of commercial and cultural space, will provide a center of gravity and excitement to an area of the city that has lacked both. For now, Related’s plans for a mixed-use building modeled loosely on its Time Warner Center in New York, which houses a hotel, retail stores, offices, condominiums and a major jazz stage, have been delayed. Related won the right to build the project in 2004. Related has until February 2013 to come up with financing for the development initiative, which will almost certainly be prohibitively costly in the current market.