BRIMFIELD - The wooded valley in which MGM Resorts International wants to build a Western Massachusetts casino spreads out below a high bluff, at the end of a steep muddy road through the woods, where isolation is the chief selling point. Landowner David Callahan brought members of the media to view the land yesterday as part of his meticulous campaign to persuade the people of Brimfield that they really can have it all-the character of a small town and a slice of the Las Vegas strip. Brimfield, population about 3,500, is currently best known for its giant outdoor antique fairs, held three times a year.