Been to Mackinac Island four times in the past 60 years, twice since 2012 (one time staying two nights at Grand Hotel before new owners turned it into a day-tourist destination). What else is there? If you are interested in history, there is a restored fort in Mackinaw City. Beyond that, it depends on what you mean by "the area." For me, "the area" is the whole Upper Peninsula, my interests are geology, history, natural science, and the U.P. has kept me busy for several trips of two to six weeks in the summer. But that scope is Ironwood to Copper Harbor to Sault Sainte Marie to St Ignace, Mackinac Island and Mackinaw City, which involves a lot of travel.
There is a whole lot more to see and do in the Lower Peninsula, 25 years of living there and making summer vacation trips, never managed to see it all.