Leonard Bernstein’s absence looms over classical music and its current dilemma: superstar conductors and dwindling receipts, “crossover” CDs and spiraling sales, and the ongoing burnout between academic composers and listeners. When Bernstein began his Young People’s Concerts in early 1958, classical culture was different in ways he changed irrevocably: the concert tradition was “high culture” filtered through Europeans like Toscanini, targeted at an educated elite, and orchestras were the province of elderly white men. How quaint that all feels today…