If the Araya rim is steel I would check that brake pads work well to stop it. If the Araya rim shows no serious signs of wearing, you have no loose or cracked spokes, and the 6-speed freewheel has a large ring (34 teeth) and the rings show little to moderate wear, I would stay with that rear wheel. I'm stilling riding wheels from 1990 that perform well. I did, however, recently tightened all my spokes on those wheels to help prevent spoke breakage.
If, however, the rear wheel is showing signs of wear, I would upgrade. You may need to spread the rear dropouts to 135mm to take new rear hubs, but that is easy.