If the rims, spokes and hubs are in "pretty good" condition, and you can live with the existing gearing, why not leave it? I would be more worried about old tires; rubber deterioriates much faster than metal.
Long before the advent of 27 and 30 gear bikes, people toured with 10 and 15 gears. My Miyata 1000 (circa 1985) was a 12-speed, I think. You do not need a lot of gears to tour; you need a wide range of gears. Check whether your old five speed freewheel will give you a range that will work for you and the type of touring you are planning.