I guess it depends on a person’s interest and available space. If you are more into layout building and not so much into operations, it could get boring. However, if it is a choice between a small layout and no layout and you like switching problem solving, it could be a lot of fun for a long time.
For instance, take a look at John Grant’s Sweethome Chicago and Sweethome Alabama layouts. They are small but have a lot of operating potential
http://cs.trains.com/mrr/f/88/p/205987/2253645.aspx#2253645