The proprietor of one of Boston’s esteemed antique bookstores is coming to Newburyport and can tell if you’re stocking trash or treasure. Kenneth Gloss, proprietor of the Brattle Bookshop in Boston, will visit the Newburyport Public Library, 94 State St., for his lecture, “Is there Value in Your Old and Rare Books?,” on April 12 at 6:30 p.m. in the Program Room.