Going for walks into the Winter season Garden Theatre, in which “The New music Man” has just opened, is like wandering as a result of the fragrance counters at Bloomingdale’s: prepare to be spritzed with nostalgia from all sides. There’s the crimson-white-and-blue Playbill, for a start off, and, in position of a curtain, a russet barn façade that pieces to reveal backdrops painted in the fashion of Grant Wood’s Midwestern fantasias—all flat, rolling green hills and overgrown-broccoli trees. (The set was developed, along with the costumes, by Santo Loquasto.) Meredith Willson’s clearly show, which premièred in 1957, normally takes spot in 1912 in a modest city in Iowa, an era…