Welcome to the world of oil dilution! 60K should help if the car is running rich. Get a thicker oil film in there, switch to a good 10W/30 and change it often and see if that helps. Other then that, new rings, valve stem seals and valve guides would be about all you could do as one of those could be the culprit.
You're getting pretty good gas mileage so I wouldn't worry about it, it's not that big a problem. As for not burning any oil, be careful about this. When gas makes it's way into oil, the level can appear to rise if the car uses no oil, or it can stay the same if the car is burning oil. If you take a really long trip, like 300 miles of non-stop driving, and your oil level drops a bunch, that is your true oil level after burning off all the gas that's been diluting things. In this case, more frequent oil changes would be prudent.
Rick