With a few more years of planning and at least $170 million, three very different redevelopment projects at a trio of the city’s historic and long-vacant buildings at one of the city’s most high-profile intersections could dramatically transform a major gateway in Worcester. Those three historic buildings – the Worcester County Courthouse, the Lincoln Square Boys Club and the Worcester Memorial Auditorium – are either underway on a development project or slated for a rehabilitation in the coming months and years.