I own a 2013DS with 22k miles, and a 2016DSR with 21k miles.
The 2013 model will not accept either a Power Tank or Charge Tank, and has a limit of ~4kW of fast charging unless you go out of your way to custom install a charger. It also has cheaper bearings, suspension, and brakes, and no ABS.
The battery also offers less 15% capacity compared to 2016+ models. (Aerodynamic improvements can tweak each bike and I do recommend them no matter what you do.)
The 2013 is a fine bike and I'm commuting around SF with mine right now, but its limits are very real and if it doesn't fit your needs (maximum daily travel), it'll be better to buy the newer bike.
I would not choose a pre-2015 model for a lot of highway travel because of the suspension and bearings, whereas I can put 400 miles per day in on my supercharging DSR (with a Corbin Seat, I must admit, but the suspension is also a considerable improvement to the ride quality).