In my experience, the front bucket of my tractor, dragged backwards is just about the best thing ever at smoothing out dirt. Just adjust the angle of the bucket to either dig in a little to lower high spots, or smooth over low areas.
I've also had great results using a plate compactor on clients yards with sprinklers and lots of landscaping. the dirt was still there, but he ruts had raised it along the sides of the ruts. Just run the compactor next to the rut and the dirt fills back into the rut. Rarely have I ever had to buy or bring in more dirt to fix ruts.