It is certainly important to keep the tires balanced. It would be surprising if your's weren't balanced when they were installed. Who knows, though? Unbalanced tires are usually pretty obvious via shaking at specific speeds.
Routine tire rotation is a different matter. MAYBE you can squeeze out a few more miles, but IMO it is not worth the hassle. I always replace tires in pairs, and may rotate front/back when doing so. If you need more than that, you probably need a wheel alignment or other suspension work. Better to fix the problem rather than sweeping it under the rug via frequent rotation.
Formerly: 2005 Airstream Interstate (Sprinter 2500 T1N)
Now!: 2014 Great West Vans Legend SE (Sprinter 3500 NCV3 I4)