After so many years it's reassuring that owner Mitchell Kaplan sometimes answers the telephone at Books & Books. Aside from their many tangible qualities -- a great selection, regular readings by nationally and internationally known authors, and a cool kids' section -- the stores are distinctive because they have improved and evolved while retaining their essential charm. Last year Kaplan took the cyberspace plunge. And coming in October: a new home. Kaplan plans to move the Gables store from its present location to the Mediterranean-style historic building (265 Aragon Ave.) across the street. The move will double the size to more than 6000 square feet and allow for a courtyard cafe. All is not copacetic, though. Kaplan's smooth monotone belies his anxiety. "It's a risky time in the book business," he volunteers. It's another big investment in a literate community, whose support, the bookseller is quick to point out, has allowed his business to survive.