Hi Roy,
I rotate my wheels routinely to ensure even wear so on the time of replacing them I am able to purchase 4 new tyres of the same tread pattern.
I rotate them when I change from summer wheels to winter wheels, so after the winter period I put back on the summer wheels by putting the wheels that were on the back onto the front. This keeps the tread wear fairly even throughout. I have done this on all of cars and never had any issue with the balance being out except on one occasion after changing the wheels around I had a bit of steering wheels vibration and need to have the front left wheel rebalanced. Garages over here charge approximately 20 - 30 Euros for changing wheels around and an additional 40 or so euros to store them for you until the next seasonal change. Many drivers like myself do it them selves and store the one set of wheels in their garage or cellar.
Over here in Germany where it is mandatory to fit winter tyres for the winter the dealers and tyre fitter garages recommend rotating the wheels when refitting your winter or summer wheels unless their is a significant difference in tread wear between the front and back wheels where they would recommend fitting the better wheels on the driving axle. I average around 12,000 km a year so there is only a marginal difference in tread wear when it comes to changing my wheels around. When I fitted my summer wheels in May this year I noticed my winter wheels had very little difference in tread wear between front and back after using them for 5 months. I can measure the tread depth to let you know the difference if that would be helpful.
If you have a full size spare wheel then I suppose the issue would be how you rotate this wheel to ensure it has roughly the same wear as your other wheels. I don't have this issue as I have no spare wheel to worry about.