Does your badly worn wood floor need to be completely refinished or even replaced? Probably not, and depending on how finicky you are about how the floor looks, refinishing does not necessarily mean sanding everything back to bare wood in preparation for new stain and new urethane.
It’s sometimes possible to re-establish a pretty good finish on a traditional stained-and-sealed wood floor the easy way. Start by giving the entire area a light sanding with a hand-held electric sander and 120-grit paper to slightly roughen the surface of the existing urethane. Next, reapply stain only to worn areas, giving the whole floor and even colour. Although it’s not made specifically for this purpose, my favourite floor-fixing stain is Minwax’s Polyshades. It’s a combination urethane and stain, though I’m only using it for colour in this application. If you can’t find an exact match for the colour of your existing floor, choose one shade darker.
Let the Polyshades dry, then brush on a couple of coats of oil-based satin urethane over the entire floor, sanding lightly with 240-grit sandpaper after the first coat has dried. This remedial option doesn’t always fix things up to everyone’s satisfaction, but not much is lost by trying. It’ll save you a lot of money and hassles. And if you don’t like the look, you can always have the floor refinished in the usual noisy, dusty and smelly way.