Should a chain be replaced even if it's not stretched? This question suggests using a tool or ruler to assess chain stretch to determine when to replace a chain. I have one such tool (Park Tool CC-3), and it tells me that my chain is not stretched even to the 0.75 level (is that %?). 

My chain has at least 2,000 miles (~3,200 km) on it, so I am wondering if it should replace it just as a matter of practice (i.e., preventive care). I try to take care of the chain: wipe it down after rides, lubricate regularly (good advice here), etc. 

So is it inconceivable that the chain is still in good shape after this many miles?

Is there any other reason to replace the chain other than elongation, assuming it otherwise appears to be okay?
The 2000 miles is an estimate of when the chain will stretch.  Your chain may last longer than that.

As far as replacing it goes, I think it depends on your financial situation.  If you can easily afford a new chain, I recommend buying one.  A replaced chain means that you don't have to worry about your current chain stretching beyond the limit and damaging your bike.

If your budget makes buying a new chain difficult, you'll be all right to keep riding.  Just check the chain stretch every so often to determine when it's getting near absolutely necessary to buy a chain.