The Nevada City Council will discuss Wednesday night whether to approve a feasibility study for an underground parking garage and, perhaps down the road, a mixed-use project in the historic downtown.The plan being discussed calls for lowering the Spring Street lot behind the National Hotel, turning 22 spaces into 70 or 80 spaces. All or part of the spaces would become permit parking.The new parking lot would be covered with a 23,000 square foot pad that could be used to support space for retail, performing arts or a historical society."We would hopefully be able to eventually partner with both the …