If you're ok with how it looks and it doesn't have splinters or seem overly dry, you might not need to re-do it.
If you're going to re-finish the floors, I highly, highly recommend waxing wood floors over polishing, especially if you have pets, small children, or roommates who are likely to make a mess.
We did that at my parents house: rent a sander (for a weekend), sand down the old varnish and everything on the wood floors, and wax. From what I recall when we did it, the wax paste was supposed to last longer than the liquid kind, but was more of a pain to apply. We did it anyway.
Advantage: large dog on hardwood, with claws? Kid dropping something heavy? BIG SCRATCH from moving furniture? Buff, re-wax, no one will ever notice... whereas with a polish, a scratch will show, will catch in the light, and will look crappier... so if you're expecting a house where things might mess the floor, the wax will look nicer for longer.