I often get bored with my worlds, but that doesn't mean I restart. I only restart and begin over again when a new FTB modpack comes out that excites me. I've played three modpacks total. Ultimate for a year, Direwolf for a few months, and then Monster for probably another year now? Or close?
Typically my play style is 24/7 when I begin a new world with a new modpack, because I'm excited. Then I taper off my hours of play as time goes on. I used to play Monster from the time I awoke to the time I fell asleep, but nowadays since there isn't much more for me to do in my world, I play FTB about once or twice a week. I'm not really the most creative of builders, that's not what drives me to play, I'm more of a tech type who likes to explore and learn new mods.