Cons of Not Refinishing Worn Wood Floor?
It really depends on how tough you will be on the floors.  Big difference between a man living alone vs. a family of 8 with two dogs.  Note that the areas that are worn are probably the high traffic areas, so you will probably be hitting those the most too.

The issue is that if there isn't any sort of protective layer, the wood will wear substantially quicker.  Meaning if you just leave the floors and you really abuse the already worn layers, they may have to be sanded further down and therefor the rest of the floor has to be sanded further down.  

My suggestion is, before you move in put a couple of quick coats of poly down on the floor.  This is about $100-150 and a DIY job.  Since you are planning on having them refinished in a couple of years you can use this as a barometer if you can do it yourself in a few years (it is easier than you think as most wood is very forgiving).