For me the most important thing is that there is a sense of distance to get to the frontier. That it takes a considerable amount of time and resources to get there and that it is not something that Joe average can decide on a sunday morning to take his family for a nice picnic at the edge of colonized space. People either go there because they work for a corporation that exploits the resources or to find a life of freedom far away from established institutions. It's a bit like crossing the Atlantic Ocean from Europe to America in the 19th century. Certainly possible but not something for everyone :)