David Robertson’s first year as music director of the St. Louis Symphony has been, in musical terms, an unqualified success. Robertson’s programming was innovative, his concerts well-received, and critics noted a sharp uptick in the orchestra’s playing. But ticket sales slumped badly for the SLSO this year, a possible after-effect of a musicians’ strike in 2005, and the organization is still struggling to find a way to make itself relevant and appealing to a broader audience.